Method of forming patterns

ABSTRACT

A method of forming patterns includes (a) coating a substrate with a resist composition for negative development to form a resist film, wherein the resist composition contains a resin capable of increasing the polarity by the action of the acid and becomes more soluble in a positive developer and less soluble in a negative developer upon irradiation with an actinic ray or radiation, (b) forming a protective film on the resist film with a protective film composition after forming the resist film and before exposing the resist film, (c) exposing the resist film via an immersion medium, and (d) performing development with a negative developer.

The present application is a Continuation of U.S. application Ser. No. 14/521,622, filed Oct. 23, 2014, which is a Continuation of U.S. application Ser. No. 14/083,816 filed Nov. 19, 2013 (now U.S. Pat. No. 8,895,225), which is a Continuation of U.S. application Ser. No. 13/283,125 filed Oct. 27, 2011 (now U.S. Pat. No. 8,617,794), which is a Continuation-in-part of U.S. application Ser. No. 12/895,516 filed on Sep. 30, 2010 (now U.S. Pat. No. 8,071,272), which is a Continuation of U.S. patent application Ser. No. 12/137,232 filed on Jun. 11, 2008 (now U.S. Pat. No. 7,998,655), which claims the benefit of Japanese Patent Application No. 2007-155322 filed on Jun. 12, 2007. The entire disclosures of the prior applications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of forming patterns, which is usable in a production process of semiconductors, such as ICs, manufacturing of circuit boards for liquid crystal displays or thermal heads, and other lithography processes of photofabrication. More specifically, the invention is concerned with a method of forming patters by using a resist composition for negative development, a protective film composition for protecting a film formed from the resist composition and a negative developer in the lithography process performing light exposure by means of immersion-type projection exposure apparatus.

2. Description of the Related Art

As semiconductor devices have become increasingly finer, progress has been made in developing exposure light sources of shorter wavelengths and projection lenses having higher numerical apertures (higher NAs). Up to now, steppers using as light sources ArF excimer laser with a wavelength of 193 nm and having NA of 1.35 have been developed. As generally well known, relationships of these factors to resolution and depth of focus can be given by the following expressions; (Resolution)=k ₁(λ/NA) (Depth of Focus)=±k ₂ ·λ/NA ² where λ is the wavelength of an exposure light source, NA is the numerical aperture of a projection lens, and k₁ and k₂ are coefficients concerning a process.

As an art of heightening the resolution in an optical microscope, the method of filling the space between a projection lens and a test specimen with a liquid having a high refractive index (hereinafter referred to as an immersion liquid or an immersion medium), or the so-called immersion method, has hitherto been known.

This “immersion effect” can be explained as follows. When the immersion method is applied, the foregoing resolution and depth of focus can be given by the following expressions; (Resolution)=k ₁(λ₀ /n)/NA ₀ (Focal depth)=±k ₂(λ₀ /n)/NA ₀ ² where λ₀ is the wavelength of an exposure light source in the air, n is the refractive index of an immersion liquid relative to the air and NA₀ is equal to sine when the convergent half angle of incident rays is represented by θ. That is to say, the effect of immersion is equivalent to the use of exposure light with a 1/n wavelength. In other words, application of the immersion method to a projection optical system having the same NA value can multiply the focal depth by a factor of n.

This art is effective on all shapes of patterns, and besides, it can be used in combination with super-resolution techniques under study at present, such as a phase-shift method and an off-axis illumination method.

Examples of apparatus utilizing this effect for transfer of fine circuit patterns in semiconductor devices are disclosed in Patent Document 1 (JP-A-57-153433) and Patent Document 2 (JP-A-7-220990), but these documents have no description of resist suitable for immersion lithography.

Recent progress of immersion lithography is reported, e.g., in Non-patent Document 1 (Proc. SPIE, 4688, 11 (2002)), Non-patent Document 2 (J. Vac. Sci. Technol., B 17 (1999)), Patent Document 3 (WO 2004/077158) and Patent Document 4 (WO 2004/068242). In the case where ArF excimer laser is used as a light source, purified water (refractive index at 193 nm: 144) is the most promising immersion liquid in point of not only handling safety but also transmittance and refractive index at 193 nm, and actually applied in mass production too. On the other hand, it is known that immersion exposure using a medium of a higher refractive index as immersion liquid can offer higher resolution (Non-patent Document 3: Nikkei Microdevices, April in 2004).

For the purpose of supplementing the sensitivity of resist, which has been reduced by light absorption from the resist for KrF excimer laser (248 nm) onward, the image formation method referred to as a chemical amplification technique has been adopted as a method of patterning resist. To illustrate an image formation method utilizing chemical amplification by a positive-working case, images are formed in such a process that exposure is performed to cause decomposition of an acid generator in the exposed areas, thereby generating an acid, and conversion of alkali-insoluble groups into an alkali-soluble groups by utilizing the acid generated as a reaction catalyst is caused by bake after exposure (PEB: Post Exposure Bake) to allow the removal of exposed areas by an alkaline developer.

Since application of immersion lithography to chemical amplification resist brings the resist layer into contact with an immersion liquid at the time of exposure, it is pointed out that the resist layer suffers degradation and ingredients having adverse effects on the immersion liquid are oozed from the resist layer. More specifically, Patent Document 4 (WO 2004/068242) describes cases where the resists aimed at ArF exposure suffer changes in resist performance by immersion in water before and after the exposure, and indicates that such a phenomenon is a problem in immersion lithography.

As a solution to avoidance of this problem, a method of keeping resist from direct contact with water by providing a protective film (hereinafter referred to as a topcoat or an overcoat too) between the resist and a lens is known (e.g., in Patent Documents 5 to 7: WO 2004/074937, WO 2005/019937, and JP-A-2005-109146).

In such a method, it is required for the topcoat to have no solubility in immersion liquid, transparency to light from an exposure light source and a property of not causing intermixing with a resist layer and ensuring stable coating on the top of a resist layer, and besides, from the viewpoint of pattern formation by as-is utilization of an existing process, it is preferable that the topcoat has properties of easily dissolving in an alkaline aqueous solution as a developer and allowing removal simultaneous with removal of a resist layer by development.

However, topcoat-utilized image formation methods hitherto known fail to fully satisfy performance capabilities required for immersion lithography. For example, the pattern formation methods using topcoats hitherto known cause problems of development defects appearing after development and degradation in line edge roughness, and they are in need of improvements.

At present, an aqueous alkali developer containing 2.38 mass % of TMAH (tetramethylammonium hydroxide) has broad use as developers for g-ray, i-ray, KrF, ArF, EB and EUV lithographic processes.

As a developer other than the aqueous alkali developer, the developer used for performing development by dissolving exposed areas of a resist material reduced in molecular weight through cleavage of its polymer chains upon irradiation with radiation, and that characterized by having at least two functional groups of more than one kind chosen from an acetic acid group, a ketone group, an ether group or a phenyl group and a molecular weight of 150 or above, is disclosed, e.g., in Patent Document 8 (JP-A-2006-227174). In addition, the developers used for performing development by dissolving exposed areas of specified resist materials containing fluorine atoms and chosen from supercritical fluids, halogenated organic solvents or non-halogenated organic solvents are disclosed in Patent Document 9 (JP-T-2002-525683, the term “JP-T” as used herein means a published Japanese translation of a PCT patent application) and Patent Document 10 (JP-T-2005-533907).

However, as the semiconductor devices become finer, it becomes exceedingly difficult to find combinations of, e.g., a resist composition, a developer and a protective film (topcoat) composition appropriate to formation of patterns with synthetically good quality, and it is required to find pattern formation methods which can achieve, e.g., reduction in development defects appearing after development and satisfactory line edge roughness and can be applied suitably to topcoat-utilized immersion lithography.

SUMMARY OF THE INVENTION

The invention aims to solve the aforesaid problems and to provide a pattern formation method which allows not only reduction in development defects appearing after development but also reduction in line edge roughness and ensures consistent formation of high-accuracy fine patterns for fabrication of high-integration, high-precision electronic devices.

The following are aspects of the invention, and thereby the aforesaid aims of the invention are achieved.

<1> A method of forming patterns, comprising:

(a) coating a substrate with a resist composition for negative development to form a resist film, wherein the resist composition contains a resin capable of increasing the polarity by the action of the acid and becomes more soluble in a positive developer and less soluble in a negative developer upon irradiation with an actinic ray or radiation,

(b) forming a protective film on the resist film with a protective film composition after forming the resist film and before exposing the resist film,

(c) exposing the resist film via an immersion medium, and

(d) performing development with a negative developer.

<2> The method of forming patterns of <1>, wherein

the negative developer in the process (d) of performing development contains an organic solvent.

<3> The method of forming patterns of <1>, wherein

the process (d) of performing development comprises a process of removing the protective film composition and soluble portions of the resist film at the same time.

<4> The method of forming patterns of <1>, further comprising:

(e) performing development with a positive developer.

<5> The method of forming patterns of <1>, wherein

the protective film has a rate of dissolution into the negative developer in a range of 1 nm/sec to 300 run/sec.

<6> The method of forming patterns of <1>, wherein

the protective film composition contains a resin having at least either a fluorine atom or a silicon atom.

<7> The method of forming patterns of <1>, wherein

the protective film composition contains a solvent different from the negative developer.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is schematic diagrams showing relations of exposure amounts to positive development and negative development according to methods in related art, respectively;

FIG. 2 is a schematic diagram illustrating a pattern formation method which utilizes a combination of positive development and negative development; and

FIG. 3 is a schematic diagram showing a relation of exposure amounts to the positive development and negative development.

DETAILED DESCRIPTION OF THE INVENTION

Best modes for carrying out the invention are described below.

Incidentally, the term “group (atomic group)” used in this specification is intended to include both unsubstituted and substituted ones when neither a word of substituted nor a word of unsubstituted is added thereto. For instance, the term “an alkyl group” is intended to include not only an alkyl group having no substituent (an unsubstituted alkyl group) but also an alkyl group having a substituent or substituents (a substituted alkyl group).

To begin with, explanations for terms used in this specification are given. There are two modes of pattern formation, a positive mode and a negative mode, and both modes utilize a change caused in developer solubility of resist film by chemical reaction for which irradiation with light acts as a trigger, and more specifically, a case where irradiated portions dissolve in a developer is referred to as the positive mode, and a case where non-exposed portions dissolve in a developer is referred to as the negative mode. As to developers used therein, there are two types of developers, a positive developer and a negative developer. The term “positive developer” is defined as a developer allowing selective dissolution and removal of portions given exposure amounts (which are shown by a dotted line in FIG. 1) above a certain threshold value as shown by a solid line in FIG. 1, while the term “negative developer” is defined as a developer allowing selective dissolution and removal of portions given exposure amounts below the aforementioned certain threshold value. The development process using a positive developer is referred to as positive development (or a positive development process too), and the development process using a negative developer is referred to as negative development (or a negative development process too). The term multiple development (or a multiple development process) refers to the development mode utilizing a combination of the development process using a positive developer and the development process using a negative developer. In the invention, a resist composition used in negative development is referred to as a resist composition for negative development, and a resist composition used in multiple development is referred to as a resist composition for multiple development. The simple wording “a resist composition” as used hereinafter indicates a resist composition for negative development. The term “a rinse liquid for negative development” means a rinse liquid which contains an organic solvent and is used in a cleaning process after a negative development process. The term “a protective film composition” (referred to as a topcoat composition too) means a resin composition capable of forming a protective film (referred to as a topcoat too) which is insoluble in water and can be peeled off, preferably with a negative developer.

As an suitable art for a topcoat process in immersion lithography, the invention provides a new method of pattern formation utilizing a combination of (a) a process of coating a substrate with a resist composition for negative development which contains a resin capable of increasing the polarity by the action of an acid to form a film to become more soluble in a positive developer (preferably an alkali developer) and less soluble in a negative developer (preferably an organic developer) upon irradiation with an actinic ray or radiation, (b) a process of forming a protective film on the resist film with a protective film composition after forming the resist film and before exposing the resist film, (c) a process of performing immersion exposure of the resist film protected by the protective film and (d) a negative development process using a developer (a negative developer) which allows selective dissolution and removal of portions given exposure amounts below a specified threshold value (b) as shown in FIG. 3.

It is preferable that the present method of pattern formation further has (e) a process of performing development with a positive developer.

It is also preferable that the present method of pattern formation further has (f) a heating process after the immersion exposure process (c).

In the present method of pattern formation, the immersion exposure process (c) can be repeated two or more times.

In the present method of pattern formation, the heating process (f) can also be repeated two or more times.

Requirements for carrying out the invention include (i) a resist composition for negative development which contains a resin capable of increasing the polarity by the action of the acid and becomes more soluble in a positive developer and less soluble in a negative developer upon irradiation with an actinic ray or radiation, (ii) a negative developer (preferably an organic developer) and (iii) a protective film composition forming a protective film insoluble in an immersion medium (preferably water).

For performing the invention, it is favorable that (iv) a positive developer (preferably an alkali developer) is further used.

For performing the invention, it is also favorable that (v) an organic solvent-containing rinse liquid for negative development is further used.

The resist composition for negative development as used in the invention is a resin composition containing a resin capable of increasing the polarity by the action of an acid and forming a film which becomes more soluble in a positive developer and less soluble in a negative developer upon irradiation with an actinic ray or radiation. Therefore, the present resist composition for negative development can be used suitably for pattern formation through multiple development utilizing a combination of a developer (a positive developer) allowing selective dissolution and removal of portions given exposure amounts above a specified threshold value (a), a developer (a negative developer) allowing selective dissolution and removal of portions given exposure amounts below a differently specified threshold value (b) and a resist composition for negative development.

More specifically, when pattern elements on an exposure mask are projected onto a wafer coated with a resist film with irradiation with light, as shown in FIG. 3, a pattern with resolution equivalent to double the spatial frequency of the optical image (light intensity distribution) can be formed through selective dissolution and removal of regions irradiated with light of high intensities (resist portions given exposure amounts above the specified threshold value (a)) by use of a positive developer and selective dissolution and removal of regions irradiated with light of low intensities (resist portions given exposure amounts below the specified threshold value (b)) by use of a negative developer.

When the pattern formation process using two types of developers, a positive developer and a negative developer, is carried out, the sequence of these developments has no particular restriction, and more specifically, it is appropriate that development be carried out using either a positive developer or a negative developer after exposure is performed, and then negative or positive development be carried out using a developer different from the developer used in the first development. And it is preferable that, after the negative development, cleaning with an organic solvent-containing rinse liquid for negative development is carried out. By the cleaning with a rinse liquid containing an organic solvent after negative development, more satisfactory pattern formation becomes possible.

The pattern formation method for carrying out the invention is described below in more detail.

<Method of Pattern Formation>

The present method of pattern formation include the following processes. It is preferred that these processes be included in the order as described below.

More specifically, the present method of pattern formation is characterized by including sequentially:

(a) a process of coating a substrate with a resist composition for negative development to form a resist film, wherein the resist composition contains a resin capable of increasing the polarity by the action of the acid and becomes more soluble in a positive developer and less soluble in a negative developer upon irradiation with an actinic ray or radiation,

(b) forming a protective film on the resist film with a protective film composition after forming the resist film and before exposing the resist film,

(c) a process of exposing the resist film via an immersion medium, and

(d) a process of performing development with a negative developer.

It is preferred that the present method of pattern formation further include (e) a process of forming a resist pattern by performing development with a positive developer. By including this process, a pattern with resolution equivalent to double the spatial frequency can be formed.

The process (a) of a coating a substrate with a resist composition for negative development, which contains a resin capable of increasing the polarity by the action of the acid and becomes more soluble in a positive developer and less soluble in a negative developer upon irradiation with an actinic ray or radiation, may be performed using any method as long as it allows coating a substrate with the resist composition. Examples of such a method include coating methods hitherto known, such as a spin coating method, a spraying method, a roller coating method and a dip coating method. For applying a coating of resist composition, a spin coating method is preferable to the others. After application of a coating of resist composition, the substrate is heated (pre-baked) as required. By this heating, it becomes possible to evenly form the coating from which undesired residual solvents are eliminated. The pre-bake temperature has no particular limitations, but it is preferably from 50° C. to 160° C., far preferably from 60° C. to 140° C.

The substrate on which resist film is formed has no particular restrictions in the invention, and it is possible to use any of inorganic substrates made from silicon, SiN, SiO₂ and the like, coating-type inorganic substrates including SOG, and substrates generally used in lithographic processes for production of semiconductors, such as ICs, and circuit boards of liquid crystal displays, thermal heads and the like, and photofabrication of other devices.

Before the resist film is formed, the substrate may be coated with an antireflective film in advance.

As the antireflective film, any of inorganic ones formed from titanium, titanium oxide, titanium nitride, chromium oxide, carbon and amorphous silicon, respectively, and organic ones formed from, e.g., a combination of a light absorbent and a polymeric material can be used. In addition, commercially available organic antireflective films including DUV-30 series and DUV-40 series manufactured by Brewer Science Inc., AR-2, AR-3 and AR-5 manufactured by Shipley Company, and ARC series, such as ARC29A, manufactured by Nissan Chemical Industries, Ltd. can also be used.

There is no particular restriction on a resist composition which can be used in the invention so long as the composition contains a resin capable of increasing the polarity by the action of the acid and becomes more soluble in a positive developer and less soluble in a negative developer upon irradiation with an actinic ray or radiation, but it is preferred that the composition be usable in exposure to light with wavelengths of 250 nm or shorter, and it is far preferred that the composition be usable in exposure to light with wavelengths of 200 nm or shorter. Examples of such a composition include compositions containing resins having alicyclic hydrocarbon groups as illustrated hereinafter.

After the resist film formation process (a), and that before the exposure process (c) performed via an immersion medium, the process (b) is carried out where a protective film (hereinafter referred to as “a topcoat” too) is formed on the resist film by use of a protective film composition. In the process (b), a topcoat is provided between the resist film and the immersion liquid so that the resist film is not brought to direct contact with the immersion liquid. Properties required for functionality of the topcoat include suitability for coating the resist film, transparency to radiant rays, notably radiation of 193 nm, and poor solubility in an immersion liquid (preferably water). And it is preferred that the topcoat cause no mixing with the resist and be applicable evenly to the upper resist layer.

In order to apply a protective film evenly to the top of the resist film without dissolving the resist film, it is preferred that the protective film composition contain a solvent in which the resist film is insoluble. And it is far preferred that a solvent different from a constituent solvent of the negative developer as described hereinafter be used as the solvent in which the resist film is insoluble. The protective film composition has no particular restriction as to the coating method thereof. For example, it can be applied by use of a spin coating method.

In point of transparency to 193 nm, the protective film composition preferably contains a resin having no aromatic groups, specifically a resin containing at least either a fluorine atom or a silicon atom as mentioned hereinafter. However, there is no particular restriction on the resin so long as it can be dissolved in a solvent in which the resist film is insoluble.

The thickness of the topcoat has no particular limitations, but the topcoat is formed so that the thickness thereof is generally from 1 nm to 300 nm, preferably from 10 nm to 150 nm, in point of transparency to an exposure light source used.

After formation of the topcoat, the substrate is heated as required.

From the viewpoint of resolution, it is preferred that the topcoat have a refractive index close to that of the resist film.

The topcoat is preferably insoluble in an immersion liquid, far preferably insoluble in water.

As to the receding contact angle of the topcoat (protective film), it is appropriate from the viewpoint of an ability to follow an immersion liquid that the receding contact angle (at 23° C.) of an immersion liquid with respect to the protective film be from 50 degrees to 100 degrees, preferably from 60 degrees to 80 degrees. And it is preferable that the receding contact angle (at 23° C.) of water with respect to the protective film be from 50 degrees to 100 degrees, particularly from 60 degrees to 80 degrees.

In the immersion exposure process, it is required for the immersion liquid to move over a wafer while following the movement of an exposure head for scanning the wafer at a high speed to form an exposure pattern. Therefore, the contact angle of an immersion liquid in a dynamic state with respect to the topcoat becomes important and, for achievement of better resist performance, it is appropriate that the receding contact angle be within the range specified above.

For stripping off the topcoat, a negative developer may be used, or a stripping agent may be used separately. As the stripping agent, a solvent low in permeability into the resist is suitable. In point of possibility of performing the stripping-off process simultaneously with the resist development process, it is advantageous for a negative developer (preferably an organic solvent) to be able to strip off the topcoat. The negative developer used for the stripping has no other particular restrictions so long as it allows dissolution and removal of low exposure portions of the resist, and it can be selected from developers containing polar solvents, such as ketone solvents, ester solvents, alcohol solvents, amide solvents and ether solvents, or developers containing hydrocarbon solvents. Of these developers, those containing ketone solvents, ester solvents, alcohol solvents or ether solvents are preferable to the others, developers containing ester solvents are far preferred, and developers containing butyl acetate are especially preferred. From the viewpoint of stripping off the topcoat with a negative developer, the rate of dissolution of the topcoat in a negative developer is preferably from 1 nm/sec to 300 nm/sec, far preferably from 10 nm/sec to 100 nm/sec.

The expression of “rate of dissolution of the topcoat in a negative developer” used herein refers to the rate of decrease in thickness of the topcoat during exposure to the developer after formation of the topcoat, which is represented by the rate of thickness decrease during the immersion of the topcoat in a 23° C. butyl acetate solution.

When the rate of dissolution of the topcoat in a negative developer is adjusted to 1 nm/sec or above, preferably 10 nm/sec or above, the effect of reducing development defects occurring after development of the resist is produced. On the other hand, adjustment of the foregoing rate to 300 nm/sec or below, preferably 100 nm/sec or below, produces the effect of improving line edge roughness of patterns of the developed resist, probably under the influence of reduction in unevenness of exposure during the immersion exposure.

The topcoat may be removed by use of another known developer, e.g., an aqueous alkali solution. An example of an aqueous alkali solution usable for the removal is an aqueous solution of tetramethylammonium hydroxide.

In the process (c) for exposure via an immersion medium, the exposure of resist film to light can be carried out in accordance with a generally well-known method. And it is appropriate that irradiation of the resist film with an actinic ray or radiation passing through a given mask be performed via an immersion liquid. The setting of an exposure amount, though can be made as appropriate, is generally from 1 to 100 mJ/cm².

The wavelengths of a light source usable in exposure apparatus are not particularly limited in the invention, but it is preferred that the wavelengths of light emitted from a light source used be 250 nm or below. Examples of such light include KrF excimer laser light (248 nm), ArF excimer laser light (193 nm), F2 excimer laser light (157 nm), EUV light (13.5 nm) and electron beams. Among them, ArF excimer laser light (193 nm) is used to greater advantage.

When the immersion exposure is carried out, a process of cleaning the film surface with an aqueous chemical may be carried out (1) after film formation on the substrate and before the exposure process, and/or (2) after the process of exposing the film to light via an immersion liquid and before the process of heating the film.

The suitable liquid as an immersion liquid is a liquid that is transparent at the wavelength of exposure light and has the smallest possible temperature coefficient of reflective index so that distortion of optical images projected onto the film is minimized. In a special case where the exposure light source is ArF excimer laser light (193 nm), water is preferably used as the immersion liquid in terms of availability and ease of handling in addition to the foregoing viewpoints.

When water is used, an additive (liquid) capable of reducing the surface tension of water and enhancing surface activity may be added in a slight amount. Such an additive is preferably a liquid in which the resist layer on a wafer has no solubility, and besides, which has negligible influence on an optical coat provided on the under side of lens element. As water used, distilled water is suitable. Alternatively, pure water obtained by further filtering the distilled water through an ion exchange filter or the like may be used. The use of such water allows prevention of distortion caused in optical images projected onto the resist by contamination with impurities.

In the sense that further rise in refractive index is possible, a medium having a refractive index of 1.5 or above can also be used. Such a medium may be a water solution or an organic solvent.

In the present method of pattern formation, the exposure process may be carried out two or more times. In this case, two or more exposures may be performed by means of the same light source or different light sources. The first exposure is preferably performed using ArF excimer laser light (193 nm).

After performing the exposure process, it is preferable to carry out (f) a heating process (referred to as bake or PEB too), and then development and rinse are carried out. By these processes, patterns of good quality can be obtained. The PEB temperature has no particular limitations so long as resist patterns of good quality are formed, and it is generally within the range of 40° C. to 160° C.

In the invention, (d) development is carried out using a negative developer, and thereby a resist pattern is formed. It is preferred that the process (d) in which development is carried out using a negative developer be a process of removing soluble portions of the resist film and the topcoat at the same time.

When the negative development is carried out, an organic developer containing an organic solvent is preferably used.

The organic developer usable in carrying out negative development is a polar solvent, such as a ketone solvent, an ester solvent, an alcohol solvent, an amide solvent or an ether solvent, or a hydrocarbon solvent. Examples of a ketone solvent usable therein include 1-octanone, 2-octanone, 1-nonanone, 2-nonanone, acetone, 4-heptanone, methyl amyl ketone (IUPAC name: 2-heptanone), 1-hexanone, 2-hexanone, diisobutyl ketone, cyclohexanone, methylcyclohexanone, phenylacetone, methyl ethyl ketone, methyl isobutyl ketone, acetylacetone, acetonylacetone, ionone, diacetonyl alcohol, acetyl carbinol, acetophenone, methyl naphthyl ketone, isophorone and propylene carbonate; and examples of an ester solvent usable therein include methyl acetate, butyl acetate, ethyl acetate, isopropyl acetate, amyl acetate, propylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, ethyl-3-ethoxypropionate, 3-methoxybutyl acetate, 3-methyl-3-methoxybutyl acetate, methyl formate, ethyl formate, butyl formate, propyl formate, ethyl lactate, butyl lactate and propyl lactate.

Examples of an alcohol solvent usable therein include alcohol compounds, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, isobutyl alcohol, n-hexyl alcohol, n-heptyl alcohol, n-octyl alcohol and n-decanol; glycol solvents, such as ethylene glycol, diethylene glycol and triethylene glycol; and glycol ether solvents, such as ethylene glycol monomethyl ether, propylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monoethyl ether, diethylene glycol monomethyl ether, triethylene glycol monoethyl ether and methoxymethyl butanol.

Examples of an ether solvent usable therein include dioxane and tetrahydrofuran in addition to the glycol ether solvents as recited above.

Examples of an amide solvent usable therein include N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, hexamethylphosphoric triamide and 1,3-dimethyl-2-imidazolidinone.

Examples of a hydrocarbon solvent usable therein include aromatic hydrocarbon solvents, such as toluene and xylene, and aliphatic hydrocarbon solvents, such as pentane, hexane, octane and decane.

The solvents as recited above may be used as mixtures of two or more thereof, or as mixtures with other solvents or water.

As to the development methods, there are a method of developing by mounding a developer on a substrate surface by surface tension and leaving the developer at rest for a fixed period of time (puddle method), a method of spraying a developer on a substrate surface (spray method) and a method of keeping on dispensing a developer onto a substrate spinning at a constant speed while scanning the substrate at a constant speed with a developer dispense nozzle (dynamic dispense method).

The vapor pressure of a negative developer at 20° C. is preferably 5 kPa or below, far preferably 3 kPa or below, particularly preferably 2 kPa or below. By adjusting the vapor pressure of a negative developer to 5 kPa or below, evaporation of the developer on the substrate or inside a development cup can be controlled, and thereby in-plane temperature uniformity of a wafer is improved to result in improvement of in-plane dimensional uniformity of a wafer.

Examples of a negative developer having a vapor pressure of 5 kPa or below at 20° C. include ketone solvents, such as 1-octanone, 2-octanone, 1-nonanone, 2-nonanone, 4-heptanone, methyl amyl ketone (IUPAC name: 2-heptanone), 2-hexanone, diisobutyl ketone, cyclohexanone, methylcyclohexanone, phenylacetone and methyl isobutyl ketone; ester solvents, such as butyl acetate, amyl acetate, propylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, ethyl-3-ethoxypropionate, 3-methoxybutyl acetate, 3-methyl-3-methoxybutyl acetate, butyl formate, propyl formate, ethyl lactate, butyl lactate and propyl lactate; alcohol solvents, such as n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, isobutyl alcohol, n-hexyl alcohol, n-heptyl alcohol, n-octyl alcohol and n-decanol; glycol solvents, such as ethylene glycol, diethylene glycol and triethylene glycol; and glycol ether solvents, such as ethylene glycol monomethyl ether, propylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monoethyl ether, diethylene glycol monomethyl ether, triethylene glycol monoethyl ether and methoxymethyl butanol; ether solvents, such as tetrahydrofuran; amide solvents, such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide and N,N-dimethylformamide; aromatic hydrocarbon solvents, such as toluene and xylene; and aliphatic hydrocarbon solvents, such as octane and decane.

Examples of a negative developer which has its vapor pressure in the especially preferable range of 2 kPa or below at 20° C. include ketone solvents, such as 1-octanone, 2-octanone, 1-nonanone, 2-nonanone, 4-heptanone, methyl amyl ketone (IUPAC name: 2-heptanone), 2-hexanone, diisobutyl ketone, cyclohexanone, methylcyclohexanone and phenylacetone; ester solvents, such as butyl acetate, amyl acetate, propylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, ethyl-3-ethoxypropionate, 3-methoxybutyl acetate, 3-methyl-3-methoxybutyl acetate, ethyl lactate, butyl lactate and propyl lactate; alcohol solvents, such as n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, isobutyl alcohol, n-hexyl alcohol, n-heptyl alcohol, n-octyl alcohol and n-decanol; glycol solvents, such as ethylene glycol, diethylene glycol and triethylene glycol; and glycol ether solvents, such as ethylene glycol monomethyl ether, propylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monoethyl ether, diethylene glycol monomethyl ether, triethylene glycol monoethyl ether and methoxymethyl butanol; amide solvents, such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide and N,N-dimethylformamide; aromatic hydrocarbon solvents, such as xylene; and aliphatic hydrocarbon solvents, such as octane and decane.

To a developer which can be used when negative development is carried out, a surfactant can be added in an appropriate amount, if needed.

The developer has no particular restriction as to the surfactant added thereto, so addition of, e.g., an ionic or nonionic surfactant containing at least one fluorine atom and/or at least one silicon atom may be made. Examples of such an ionic or nonionic surfactant include the surfactants disclosed in JP-A-62-36663, JP-A-61-226746, JP-A-61-226745, JP-A-62-170950, JP-A-63-34540, JP-A-7-230165, JP-A-8-62834, JP-A-9-54432, JP-A-9-5988, and U.S. Pat. Nos. 5,405,720, 5,360,692, 5,529,881, 5,296,330, 5,436,098, 5,576,143, 5,294,511 and 5,824,451. Of these surfactants, nonionic surfactants are preferable to the others. Though no particular restrictions are imposed on such nonionic surfactants, it is far preferable to use a surfactant containing at least one fluorine atom or a surfactant containing at least one silicon atom.

The amount of a surfactant used is generally from 0.001 to 5 mass %, preferably from 0.005 to 2 mass %, far preferably from 0.01 to 0.5 mass %, of the total amount of the developer to which the surfactant is added.

Examples of a development method applicable herein include a method of dipping a substrate for a predetermined period of time into a tank filled with a developer (dip method), a method of developing by mounding a developer on a substrate surface by surface tension and leaving the developer at rest for a fixed period of time (puddle method), a method of spraying a developer on a substrate surface (spray method) and a method of keeping on dispensing a developer onto a substrate spinning at a constant speed while scanning the substrate at a constant speed with a developer dispense nozzle (dynamic dispense method).

After the process of negative development, a process of stopping the development while replacing the negative developer with another solvent may be carried out.

After the completion of the negative development, the present method preferably includes a cleaning process using an organic solvent-containing rinse liquid for negative development.

The rinse liquid used in the rinse process after negative development has no particular restrictions so long as it does not dissolve resist patterns, and solutions containing general organic solvents can be used. More specifically, the solution suitably used as the rinse liquid is a solution containing at least one kind of organic solvent chosen from hydrocarbon solvents, ketone solvents, ester solvents, alcohol solvents, amide solvents or ether solvents. And it is preferable that, after negative development, the cleaning process is carried out using a rinse liquid containing at least one kind of solvent chosen from ketone solvents, ester solvents, alcohol solvents or amide solvents. It is preferable by far that, after negative development, the cleaning process is carried out using a rinse liquid containing an alcohol solvent or an ester solvent, and it is especially preferable that, after negative development, the cleaning process is carried out using a rinse liquid containing monohydric alcohol. Herein, the monohydric alcohol used in the rinse process after the negative development may have any of straight-chain, branched or cyclic forms, with examples including 1-butanol, 2-butanol, 3-methyl-1-butanol, tert-butyl alcohol, 1-pentanol, 2-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 2-hexanol, 2-heptanol, 2-octanol, 3-hexanol, 3-heptanol, 3-octanol and 4-octanol. Of these alcohol solvents, 1-hexanol, 2-hexanol, 1-heptanol and 3-methyl-1-butanol are preferred over the others.

The ingredients recited above may be used as combinations of two or more thereof, or may be used as mixtures of organic solvents other than the above-recited ones.

The water content in the rinse liquid is preferably 10 mass % or below, far preferably 5 mass % or below, particularly preferably 3 mass % or below. By controlling the water content to 10 mass % or below, satisfactory developing properties can be attained.

The vapor pressure of the rinse liquid used after negative development, as measured at 20° C., is preferably from 0.05 kPa to 5 kPa, far preferably from 0.1 kPa to 5 kPa, especially preferably from 0.12 kPa to 3 kPa. By adjusting the vapor pressure of the rinse liquid to the range of 0.05 kPa to 5 kPa, in-plane temperature uniformity of a wafer is enhanced, and besides, wafer swelling caused by penetration of the rinse liquid can be controlled; as a result, in-plane dimensional uniformity of a wafer can be improved.

It is also possible to use the rinse liquid to which a surfactant is added in an appropriate amount.

In the rinse process, the wafer having undergone the negative development is subjected to cleaning treatment with the organic solvent-containing rinse liquid. There is no particular restriction on the method for the cleaning treatment. For example, a method of keeping on coating a substrate spinning at a constant speed with a rinse liquid (spin coating method), a method of dipping a substrate in a tank filled with a rinse liquid (dip method) and a method of spraying a rinse liquid onto the substrate surface (spray method) can be applied thereto. However, it is preferred that the cleaning treatment be performed by the spin coating method and then the rinse liquid be eliminated from the substrate by spinning the substrate at revs ranging from 2,000 rpm to 4,000 rpm.

In the invention, it is preferable that resist patterns are formed by further performing (e) development with a positive developer.

As the positive developer, an alkali developer can be used to advantage. Examples of such an alkali developer include alkaline aqueous solutions of inorganic alkalis such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, sodium metasilicate and aqueous ammonia, primary amines such as ethylamine and n-propylamine, secondary amines such as diethylamine and di-n-butylamine, tertiary amines such as triethylamine and methyldiethylamine, alcoholamines such as dimethylethanolamine and triethanolamine, quaternary ammonium salts such as tetramethylammonium hydroxide and tetraethylammonium hydroxide, and cyclic amines such as pyrrole and piperidine. Of these alkaline aqueous solutions, an aqueous solution of tetraethylammonium hydroxide is preferred over the others.

The alkali developers as recited above may also be used after alcohol compounds and surfactants are further added in appropriate amounts.

The alkali concentration of an alkali developer is generally from 0.01 to 20 mass %.

The pH of an alkali developer is generally from 10.0 to 15.0.

The time to perform development with an alkali developer is generally from 10 to 300 seconds.

The alkali concentration (and pH) of an alkali developer and the development time can be adjusted as appropriate according to patterns to be formed.

As a rinse liquid used in the rinse process carried out after the positive development, purified water is used. Alternatively, purified water to which a surfactant is added in an appropriate amount may be used.

Further, it is possible to carry out treatment with a supercritical fluid after development processing or rinse processing for the purpose of eliminating the developer or the rinse liquid adhering to patterns.

Furthermore, it is possible to carry out heat treatment after the treatment with a supercritical fluid for the purpose of eliminating water remaining in patterns.

Resist compositions for negative development, which are usable in the invention, are described below.

<Resist Composition for Negative Development>

(A) Resin that can Increase in Polarity by Action of Acid

The resin usable in a resist composition according to the invention and capable of increasing in the polarity by the action of an acid is a resin having groups capable of decomposing by the action of an acid to produce alkali-soluble groups (hereinafter referred to as “acid-decomposable groups”) in either its main chain, or side chains, or both (hereinafter referred to as “an acid-decomposable resin”, “an acid-decomposable Resin (A)” or “a Resin (A)”), and preferably a resin having mononuclear or polynuclear alicyclic hydrocarbon structures and capable of increasing its polarity, increasing its solubility in an alkali developer and decreasing its solubility in an organic solvent by the action of an acid (hereinafter referred to as “an alicyclic hydrocarbon-containing acid-decomposable resin”). Reasons for those changes are not clear, but as a reason it is likely thought that the resin causes a great change in polarity by undergoing the irradiation with an actinic ray or radiation to result in enhancement of dissolution contrasts in both the case of development with a positive developer (preferably an alkali developer) and the case of development with a negative developer (preferably an organic solvent). Further, it is thought that, because of high hydrophobicity of the resin having mononuclear or polynuclear aliphatic hydrocarbon structures, the developability enhancement is caused in the case where resist film regions low in irradiation intensity are developed with a negative developer (preferably an organic solvent).

The present resist composition containing a resin capable of increasing the polarity by the action of an acid can be used suitably for the case of irradiation with ArF excimer laser.

The acid-decomposable resin includes a unit having an acid-decomposable group.

A group suitable as the group capable of decomposing by the action of an acid (the acid-decomposable group) is a group obtained by substituting a group capable of splitting off by the action of an acid for a hydrogen atom of an alkali-soluble group.

Examples of alkali-soluble groups include groups respectively having a phenolic hydroxyl group, a carboxylic acid group, a fluorinated alcohol group, a sulfonic acid group, a sulfonamido group, a sulfonylimido group, an (alkylsulfonyl)(alkylcarbonyl)methylene group, an (alkylsulfonyl) (alkylcarbonyl)imido group, a bis(alkylcarbonyl)methylene group, a bis(alkylcarbonyl)imido group, a bis(alkylsulfonyl)methylene group, a bis(alkylsulfonyl)imido group, a tris(alkylcarbonyl)methylene group and a tris(alkylsulfonyl)methylene group.

Of these alkali-soluble groups, a carboxylic acid group, a fluorinated alcohol group (preferably a hexafluoroisopropanol group) and a sulfonic acid group are preferred over the others.

Examples of a group capable of splitting off by the action of an acid include groups of formula —C(R₃₆)(R₃₇)(R₃₈), groups of formula —C(R₃₆)(R₃₇)(OR₃₉), and groups of formula —C(R₀₁)(R₀₂)(OR₃₉).

In these formulae, R₃₆ to R₃₉ each represent an alkyl group, a cycloalkyl group, an aryl group, an aralkyl group or an alkenyl group independently. R₃₆ and R₃₇ may combine with each other to form a ring. R₀₁ and R₀₂ each represent a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, an aralkyl group or an alkenyl group independently.

Examples of a group suitable as an acid decomposable group include cumyl ester groups, enol ester groups, acetal ester groups and tertiary alkyl ester groups. Of these groups, tertiary alkyl ester groups are preferred over the others.

The alicyclic hydrocarbon-containing acid-decomposable resin is preferably a resin having at least one kind of repeating units selected from repeating units having alicyclic hydrocarbon-containing partial structures represented by any of the following formulae (pI) to (pV) or repeating units represented by the following formula (II-AB).

In the formulae (pI) to (pV), R₁₁ represents a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group or a sec-butyl group, and Z represents atoms forming a cycloalkyl group together with the carbon atom.

R₁₂ to R₁₆ each represent a 1-4C straight-chain or branched alkyl group, or a cycloalkyl group independently, provided that at least one of R₁₂ to R₁₄, or either R₁₅ or R₁₆ represents a cycloalkyl group.

R₁₇ to R₂₁ each represent a hydrogen atom, a 1-4C straight-chain or branched alkyl group or a cycloalkyl group independently, provided that at least one of R₁₇ to R₂₁ represents a cycloalkyl group. In addition, either R₁₉ or R₂₁ is required to represent a 1-4C straight-chain or branched alkyl group or a cycloalkyl group.

R₂₂ to R₂₅ each represent a hydrogen atom, a 1-4C straight-chain or branched alkyl group or a cycloalkyl group independently, provided that at least one of R₂₂ to R₂₅ represents a cycloalkyl group. Alternatively, R₂₃ and R₂₄ may combine with each other to form a ring.

In the formula (II-AB), R₁₁′ and R₁₂′ each represent a hydrogen atom, a cyano group, a halogen atom or an alkyl group independently.

Z′ represents atoms forming an alicyclic structure together with the two bonded carbon atoms (C—C).

The formula (II-AB) is preferably the following formula (II-AB 1) or formula (II-AB2).

In the formulae (II-AB 1) and (II-AB2), R₁₃′ to R₁₆′ each independently represent a hydrogen atom, a halogen atom, a cyano group, —COOH, —COOR₅, a group capable of decomposing by the action of an acid, —C(═O)—X-A′-R₁₇′, an alkyl group or a cycloalkyl group. At least two of R₁₃′ to R₁₆′ may combine with each other to form a ring.

Herein, R₅ represents an alkyl group, a cycloalkyl group or a group having a lactone structure.

X represents an oxygen atom, a sulfur atom, —NH—, —NHSO₂— or —NHSO₂NH—. A′ represents a single bond or a divalent linkage group.

R₁₇′ represents —COOH, —COOR₅, —CN, a hydroxyl group, an alkoxyl group, —CO—NH—R₆, —CO—NH—SO₂—R₆ or a group having a lactone structure.

R₆ represents an alkyl group or a cycloalkyl group.

n represents 0 or 1.

The alkyl group which R₁₂ to R₂₅ each can represent in the formulae (pI) to (pV) is preferably a 1-4C straight-chain or branched alkyl group.

The cycloalkyl group which R₁₁ to R₂₅ each can represent or the cycloalkyl group which can be formed of Z and the carbon atom may be monocyclic or polycyclic. Examples of such a cycloalkyl group include groups each containing at least 5 carbon atoms and having a monocyclo, bicyclo, tricyclo or tetracyclo structure. The number of carbon atoms in such a structure is preferably from 6 to 30, particularly preferably from 7 to 25. These cycloalkyl groups may have substituents.

Suitable examples of such a cycloalkyl group include an adamantyl group, a noradamantyl group, a decaline residue, a tricyclodecanyl group, a tetracyclododecanyl group, a norbornyl group, a cedrol group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclodecanyl group and a cyclododecanyl group. Of these groups, an adamantyl group, a norbornyl group, a cyclohexyl group, a cyclopentyl group, a tetracyclodecanyl group and a tricyclodecanyl group are preferred over the others.

Each of those alkyl groups and cycloalkyl groups may further have a substituent. Examples of such a substituent include an alkyl group (1-4C), a halogen atom, a hydroxyl group, an alkoxyl group (1-4C), a carboxyl group and an alkoxycarbonyl group (2-6C). Herein, the alkyl, alkoxy and alkoxycarbonyl groups each may further have a substituent, such as a hydroxyl group, a halogen atom or an alkoxyl group.

In the resins, the structures represented by the formulae (pI) to (pV) can be used for protection of alkali-soluble groups. Examples of such alkali-soluble groups include various groups known in this technical field.

More specifically, such a protected alkali-soluble group has a structure formed by substituting the structure represented by any of the formulae (pI) to (pV) for the hydrogen atom of a carboxylic acid group, a sulfonic acid group, a phenol group or a thiol group. Of these structures, structures formed by substituting the structures represented by formulae (pI) to (pV) for the hydrogen atoms of carboxylic acid groups or sulfonic acid groups are preferable to the others.

As repeating units containing alkali-soluble groups protected by the structures of formulae (pI) to (pV), repeating units represented by the following formula (pA) are suitable.

In the formula (pA), each R represents a hydrogen atom, a halogen atom or a 1-4C straight-chain or branched alkyl group. Two or more Rs may be the same or different.

A represents a single bond, an alkylene group, an ether group, a thioether group, a carbonyl group, an ester group, an amido group, a sulfonamide group, a urethane group, a urea group, or a combination of two or more of the groups recited above, preferably a single bond.

Rp₁ represents any of the formulae (pI) to (pV).

The most suitable of repeating units represented by the formula (pA) is a repeating unit derived from 2-alkyl-2-adamantyl (meth)acrylate or dialkyl(1-adamantyl)methyl (meth)acrylate.

Examples of the repeating unit having an acid-decomposable group are illustrated below, but these examples should not be construed as limiting the scope of the invention.

(In the following formulae, Rx represents H, CH₃ or CH₂OH, and Rxa and Rxb each represent a 1-4C alkyl group.)

Examples of a halogen atom which R₁₁′ and R₁₂′ each can represent in the formula (II-AB) include a chlorine atom, a bromine atom, a fluorine atom and an iodine atom.

Examples of an alkyl group which R₁₁′ and R₁₂′ each can represent in the formula (II-AB) include 1-10C straight-chain or branched alkyl groups.

The atoms Z′ for forming an alicyclic structure are atoms forming an unsubstituted or substituted alicyclic hydrocarbon as a repeating unit of the resin, particularly preferably atoms forming a bridged alicyclic hydrocarbon as a repeating unit.

Examples of a skeleton of the alicyclic hydrocarbon formed include the same skeletons as the alicyclic hydrocarbon groups represented by R₁₂ to R₂₅ in the formulae (pI) to (pV) have.

The skeleton of the alicyclic hydrocarbon may have a substituent. Examples of such a substituent include the groups represented by R₁₃′ to R₁₆′ in the formula (II-AB 1) or (II-AB2).

In the alicyclic hydrocarbon-containing acid-decomposable resin relating to the invention, groups capable of decomposing by the action of an acid can be incorporated into at least one type of repeating units chosen from repeating units having aliphatic hydrocarbon-containing partial structures represented by any of the formulae (pI) to (pV), repeating units represented by the formula (II-AB) or repeating units of copolymerization components described hereinafter. However, it is preferable that the groups capable of decomposing by the action of an acid are incorporated into repeating units having alicyclic hydrocarbon-containing partial structures represented by any of the formulae (pI) to (pV).

Various kinds of substituents as R₁₃′ to R₁₆′ in the formula (II-AB1) or (II-AB2) may also become substituents of atoms Z′ for forming an alicyclic hydrocarbon structure or a bridged alicyclic hydrocarbon structure in the formula (II-AB).

Examples of repeating units represented by the formula (II-AB 1) or (II-AB2) are illustrated below, but these examples should not be construed as limiting the scope of the invention.

The alicyclic hydrocarbon-containing acid-decomposable resin for use in the invention preferably has lactone groups. As the lactone groups, any groups can be used as long as they have lactone structures. Suitable examples of a lactone group include groups having 5- to 7-membered ring lactone structures, preferably groups in a state that 5- to 7-membered ring lactone structures fuse with other ring structures to form bicyclo or spiro structures. It is preferable by far that the alicyclic hydrocarbon-containing acid-decomposable resin for use in the invention has repeating units containing the groups having lactone structures represented by any of the following formulae (LC1-1) to (LC1-16). Alternatively, the groups having lactone structures may be bonded directly to the main chain. The lactone structures used to advantage are groups represented by the formulae (LC1-1), (LC1-4), (LC1-5), (LC1-6), (LC1-13) and (LC1-14), and the use of specified lactone structures contributes to improvements in line edge roughness and development defects.

The lactone structure moieties each may have a substituent (Rb₂) or needn't. Suitable examples of a substituent (Rb₂) include 1-8C alkyl groups, 4-7C cycloalkyl groups, 1-8C alkoxyl groups, 1-8C alkoxycarbonyl groups, a carboxyl group, halogen atoms, a hydroxyl group, a cyano group and acid-decomposable groups. n2 represents an integer of 0 to 4. When n2 is 2 or above, a plurality of Rb2s may be the same or different, or they may combine with each other to form a ring.

Examples of a repeating unit containing a group having a lactone structure represented by any of the formulae (LC1-1) to (LC1-16) include the repeating units represented by the formula (II-AB 1) or (II-AB2) wherein at least one of R₁₃′ to R₁₆′ is a group having the lactone structure represented by any of the formulae (LC1-1) to (LC 1-16) (for instance, R₅ in —COOR₅ represents a group having the lactone structure represented by any of the formulae (LC1-1) to (LC1-16)), and repeating units represented by the following formula (AI).

In the formula (AI), Rb₀ represents a hydrogen atom, a halogen atom or a 1-4C alkyl group. Examples of a suitable substituent the alkyl group of Rbo may have include a hydroxyl group and halogen atoms.

Examples of a halogen atom represented by Rb₀ include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom.

Rb₀ is preferably a hydrogen atom, a methyl group, a hydroxymethyl group or a trifluoromethyl group, and more preferably a hydrogen atom or a methyl group.

Ab represents a single bond, an alkylene group, a divalent linkage group having a mononuclear or polynuclear alicyclic hydrocarbon structure, an ether linkage, an ester linkage, a carbonyl group, or a divalent group formed by combining two or more of the groups recited above. The preferred as Ab is a single bond or a linkage group represented by -Ab₁-CO₂—. Ab₁ is a straight-chain or branched alkylene group or a mononuclear or polynuclear cycloalkylene group, preferably a methylene group, an ethylene group, a cyclohexylene group, an adamantylene group or a norbornylene group.

V represents a group represented by any of the formulae (LC1-1) to (LC 1-16).

A repeating unit having a lactone structure generally has optical isomers, and any of the optical isomers may be used. Further, one optical isomer may be used by itself, or two or more of optical isomers may be used as a mixture. When one optical isomer is mainly used, the optical purity (ee) thereof is preferably 90 or above, far preferably 95 or above.

Examples of a repeating unit containing a group having a lactone structure are illustrated below, but these examples should not be construed as limiting the scope of the invention.

(In each of the following formulae, Rx is H, CH₃, CH₂OH or CF₃)

(In each of the following formulae, Rx is H, CH₃, CH₂OH or

CF₃)

(In each of the following formulae, Rx is H, CH₃, CH₂OH or CF₃)

The alicyclic hydrocarbon-containing acid-decomposable resin for use in the invention preferably has repeating units containing organic groups having polar groups, especially repeating units having alicyclic hydrocarbon structures substituted with polar groups. By having such repeating units, the resin can contribute to enhancement of adhesiveness to a substrate and affinity for a developer. As the alicyclic hydrocarbon part of the alicyclic hydrocarbon structure substituted with a polar group, an adamantyl group, a diamantyl group or a norbornyl group is suitable. As the polar group in such a structure, a hydroxyl group or a cyano group is suitable. As the alicyclic hydrocarbon structures substituted with polar groups, partial structures represented by the following formulae (VIIa) to (VIld) are suitable.

In the formulae (VIIa) to (VIII), R_(2C) to R_(4C) each represent a hydrogen atom, a hydroxyl group or a cyano group independently, provided that at least one of them represents a hydroxyl group or a cyan group. In such partial structures, it is preferable that one of R_(2C) to R_(4C) is a hydroxyl group and the remainder are hydrogen atoms, and that two of R_(2C) to R_(4C) are hydroxyl groups and the remainder is a hydrogen atom.

In the partial structure of formula (VIIa), the case where two of R_(2C) to R_(4C) are hydroxyl groups and the remainder is a hydrogen atom is far preferred.

Examples of repeating units containing groups represented by the formulae (VIIa) to (VIId) include the repeating units represented by the formula (II-AB1) or (II-AB2) wherein at least one of R₁₃′ to R₁₆′ is a group represented by any of the formulae (VIIa) to (VIId) (for example, R₅ in —COOR₅ represents a group represented by any of the formulae (VIIa) to (VIId)), and repeating units represented by the following formulae (AIIa) to (AIId).

In the formula (AIIa) to (AIId), R_(1C) represents a hydrogen atom, a methyl group, a trifluoromethyl group or a hydroxymethyl group, and R_(2C) to R4c have the same meanings as in the formulae (VIIa) to (VIII).

Examples of repeating units represented by the formulae (AIIa) to (AIId) are illustrated below, but these examples should not be construed as limiting the scope of the invention.

The alicyclic hydrocarbon-containing acid-decomposable resin for use in the invention may have repeating units represented by the following formula (VIII).

In the formula (VIII), Z₂ represents —O— or —N(R₄₁)—. R₄₁ represents a hydrogen atom, a hydroxyl group, an alkyl group or —OSO₂—R₄₂. R₄₂ represents an alkyl group, a cycloalkyl group or a camphor residue. The alkyl groups of R₄₁ and R₄₂ may be substituted with halogen atoms (preferably fluorine atoms) or so on.

Examples of a repeating unit represented by the formula (VIII) are illustrated below, but these examples should not be construed as limiting the scope of the invention.

The alicyclic hydrocarbon-containing acid-decomposable resin for use in the invention preferably has repeating units containing alkali-soluble groups, and far preferably has repeating units containing carboxyl groups. The presence of such groups in the repeating units can enhance resolution in the use for contact hole. Suitable examples of a repeating unit containing a carboxyl group include a repeating unit containing the carboxyl group bonded directly to the main chain of resin, such as a repeating unit derived from acrylic acid or methacrylic acid, a repeating unit containing the carboxyl group attached to the main chain of resin via a linkage group, and a unit introduced as a polymer chain terminal by using a polymerization initiator or chain transfer agent having an alkali-soluble group at the time of polymerization. Therein, the linkage group may have a mononuclear or polynuclear cyclic hydrocarbon structure. Of these repeating units, those derived from acrylic acid and methacrylic acid in particular are preferred.

The alicyclic hydrocarbon-containing acid-decomposable resin for use in the invention may further have repeating units which each contain 1 to 3 groups represented by the following formula (F1). The presence of these groups contributes to improvement in line edge roughness quality.

In the formula (F1), R₅₀ to R₅₅ each represent a hydrogen atom, a fluorine atom or an alkyl group independently, provided that at least one of R₅₀ to R₅₅ is a fluorine atom or an alkyl group at least one hydrogen atom of which is substituted with a fluorine atom.

Rx represent a hydrogen atom or an organic group (preferably an acid-decomposable blocking group, an alkyl group, a cycloalkyl group, an acyl group or an alkoxycarbonyl group).

The alkyl group represented by R₅₀ to R₅₅ each may be substituted with a halogen atom such as a fluorine atom, a cyano group or so on, and suitable examples thereof include 1-3C alkyl groups, such as a methyl group and a trifluoromethyl group.

Nevertheless, it is preferable that all of R₅₀ to R₅₅ are fluorine atoms.

Suitable examples of an organic group represented by Rx include acid-decomposable blocking groups, and alkyl, cycloalkyl, acyl, alkylcarbonyl, alkoxycarbonyl, alkoxycarbonylmethyl, alkoxymethyl and 1-alkoxyethyl groups which each may have a substituent.

The repeating units containing groups represented by the formula (F1) are preferably repeating units represented by the following formula (F2).

In the formula (F2), Rx represents a hydrogen atom, a halogen atom, or a 1-4C alkyl group. The substituent the alkyl group of Rx may have is preferably a hydroxyl group or a halogen atom.

Fa represents a single bond, or a straight-chain or branched alkylene group (preferably a single bond).

Fb represents a mononuclear or polynuclear cyclic hydrocarbon group.

Fc represents a single bond, or a straight-chain or branched alkylene group (preferably a single bond or a methylene group).

F1 represents a group represented by the formula (F1).

P1 represents 1, 2 or 3.

The cyclic hydrocarbon group of Fb is preferably a cyclopentylene group, a cyclohexylene group or a norbornylene group.

Examples of the repeating unit having a group represented by the formula (F1) are illustrated below, but these examples should not be construed as limiting the scope of the invention.

The alicyclic hydrocarbon-containing acid-decomposable resin for use in the invention may further contain repeating units having alicyclic hydrocarbon structures and not showing acid decomposability. By the presence of such repeating units, elution of low molecular components from a resist coating into an immersion liquid during the performance of immersion lithography can be reduced. Examples of such repeating units include those derived from 1-adamantyl (meth)acrylate, tricyclodecanyl (meth)acrylate and cyclohexayl (meth)acrylate.

Examples of the repeating units having alicyclic hydrocarbon structures and not showing acid decomposability include repeating units containing neither a hydroxyl group nor a cyano group, and are preferably repeating units represented by the following formula (IX).

In the formula (IX), R₅ represents a hydrocarbon group having at least one cyclic structure and containing neither a hydroxyl group nor a cyano group.

Ra represents a hydrogen atom, an alkyl group or —CH₂—O—Ra₂. Herein, Ra₂ represents a hydrogen atom, an alkyl group or an acyl group. Ra is preferably a hydrogen atom, a methyl group, a hydroxymethyl group or a trifluoromethyl group, and more preferably a hydrogen atom or a methyl group.

The cyclic structure contained in R₅ may be a monocyclic hydrocarbon group or a polycyclic hydrocarbon group. Examples of the monocyclic hydrocarbon group include 3-12C cycloalkyl groups such as a cyclopentyl group, a cyclohexyl group, a cycloheptyl group and a cyclooctyl group, and 3-12C cycloalkenyl groups such as a cyclohexenyl group. Of these monocyclic hydrocarbon groups, 3-7C monocyclic hydrocarbon groups, especially a cyclopentyl group and a cyclohexyl group, are preferred over the others.

The polycyclic hydrocarbon group may be an assembled-ring hydrocarbon group or a bridged-ring hydrocarbon group. Examples of the assembled-ring hydrocarbon group include a bicyclohexyl group and a perhydronaphthalenyl group. Examples of the bridged hydrocarbon ring include bicyclic hydrocarbon rings such as a pinane ring, a bornane ring, a norpinane ring, a norbornane ring and bicyclooctane rings (e.g., a bicyclo[2.2.2]octane ring, a bicyclo[3.2.1]octane ring), tricyclic hydrocarbon rings such as a homobredane ring, an adamantane ring, a tricyclo[5.2.1.02′ 6]decane ring and a tricyclo[4.3.1.12′5]undecane ring, and tetracyclic hydrocarbon rings such as a tetracyclo[4.4.0.12′51′1° ]dodecane ring and a perhydro-1,4-methano-5,8-methanonaphthalene ring. And additional examples of the bridged hydrocarbon ring include condensed hydrocarbon rings formed by fusing together two or more of 5- to 8-membered cycloalkane rings such as perhydronaphthalene (decaline), perhydroanthracene, perhydrophenanthrene, perhydroacenaphthene, perhydrofluorene, perhydroindene and perhydrophenalene rings.

Examples of a bridged-ring hydrocarbon group suitable as the cyclic structure of R₅ include a norbornyl group, an adamantyl group, a bicyclooctanyl group and a tricyclo[5.2.1.02′6]decanyl group. Of these groups, a norbornyl group and an adamantyl group are preferred over the others.

Each of the alicyclic hydrocarbon groups recited above may have a substituent. Examples of a substituent suitable for those groups each include a halogen atom, an alkyl group, a hydroxyl group protected by a protective group, and an amino group protected by a protective group. Suitable examples of the halogen atom include bromine, chlorine and fluorine atoms. Suitable examples of the alkyl group include methyl, ethyl, butyl and t-butyl groups. These alkyl groups each may further have a substituent. Examples of the substituent include a halogen atom, an alkyl group, a hydroxyl group protected by a protective group and an amino group protected by a protective group.

Examples of such protective groups include an alkyl group, a cycloalkyl group, an aralkyl group, a substituted methyl group, a substituted ethyl group, an acyl group, an alkoxycarbonyl group and an aralkyloxycarbonyl group. Suitable examples of the alkyl group include 1-4C alkyl groups, those of the substituted methyl group include methoxymethyl, methoxythiomethyl, benzyloxymethyl, t-butoxymethyl and 2-methoxyethoxymethyl groups, those of the substituted ethyl group include 1-ethoxyethyl and 1-methyl-1-methoxyethyl groups, those of the acyl group include 1-6C aliphatic acyl groups such as formyl, acetyl, propionyl, butyryl, isobutyryl, valeryl and pivaloyl groups, and those of the alkoxycarbonyl group include 1-4C alkoxycarbonyl groups.

The proportion of repeating units represented by the formula (IX), which have neither a hydroxyl group nor a cyano group is preferably from 0 to 40 mole %, far preferably from 0 to 20 mole %, with respect to the total repeating units of the alicyclic hydrocarbon-containing acid-decomposable resin.

Examples of a repeating unit represented by the formula (IX) are illustrated below, but these examples should not be construed as limiting the scope of the invention.

In the following structural formulae, Ra represents H, CH₃,

CH₂OH or CF₃.

In addition to the repeating structural units recited above, the alicyclic hydrocarbon-containing acid-decomposable resin for use in the invention can contain a wide variety of repeating structural units for the purpose of controlling dry etching resistance, suitability for standard developers, adhesiveness to substrates, resist profile, and besides, characteristics generally required for resist, such as resolution, heat resistance and sensitivity.

Examples of such repeating structural units include repeating structural units corresponding to the monomers as recited below, but these examples should not be construed as limiting the scope of the invention.

By having those repeating units, it becomes possible to make fine adjustments to properties required for the alicyclic hydrocarbon-containing acid-decomposable resin, especially properties including:

(1) solubility in a coating solvent,

(2) film formability (glass transition temperature),

(3) solubility in a positive developer and solubility in a negative developer,

(4) thinning of film (hydrophilic-hydrophobic balance, alkali-soluble group selection),

(5) adhesion of unexposed areas to a substrate, and

(6) dry etching resistance.

Examples of monomers suitable for the foregoing purposes include compounds which each have one addition-polymerizable unsaturated bond and are selected from acrylic acid esters, methacrylic acid esters, acrylamides, methacrylamides, allyl compounds, vinyl ethers, or vinyl esters.

In addition to those monomers, any other monomers may be copolymerized so long as they are addition-polymerizable unsaturated compounds capable of forming copolymers together with monomers corresponding to the various repeating structural units mentioned above.

The ratio between mole contents of repeating structural units in the alicyclic hydrocarbon-containing acid-decomposable resin can be chosen appropriately for adjusting dry etching resistance, standard developer suitability, adhesion to substrates, resist profile, and characteristics generally required for resist, such as resolution, heat resistance and sensitivity.

Examples of a preferred state of the alicyclic hydrocarbon-containing acid-decomposable resin for use in the invention include the following.

(1) A state of containing repeating units each having an alicyclic hydrocarbon-containing partial structure represented by any of the formulae (pI) to (pV) (side-chain type).

Herein, the repeating units contained are preferably (meth)acrylate repeating units each having a structure containing any of (pI) to (pV).

(2) A state of containing repeating units represented by the formula (II-AB) (main-chain type). However, the state (2) further includes the following.

(3) A state of having repeating units represented by the formula (II-AB), maleic anhydride derivative and (meth)acrylate structures (hybrid type).

The content of repeating units having acid-decomposable groups in the alicyclic hydrocarbon-containing acid-decomposable resin is preferably from 10 to 60 mole %, far preferably from 20 to 50 mole %, further preferably from 25 to 40 mole %, of the total repeating structural units.

The content of repeating units having acid-decomposable groups in an acid-decomposable resin is preferably from 10 to 60 mole %, far preferably from 20 to 50 mole %, further preferably from 25 to 40 mole %, of the total repeating structural units.

The content of repeating units having alicyclic hydrocarbon-containing partial structures represented by the formulae (pI) to (pV) in the alicyclic hydrocarbon-containing acid-decomposable resin is preferably from 20 to 70 mole %, far preferably from 20 to 50 mole %, further preferably from 25 to 40 mole %, of the total repeating structural units.

The content of repeating units represented by the formula (II-AB) in the alicyclic hydrocarbon-containing acid-decomposable resin is preferably from 10 to 60 mole %, far preferably from 15 to 55 mole %, further preferably from 20 to 50 mole %, of the total repeating structural units.

The content of repeating units having lactone rings in an acid-decomposable resin is preferably from 10 to 70 mole %, far preferably from 20 to 60 mole %, further preferably from 25 to 40 mole %, of the total repeating structural units.

The content of repeating units containing organic groups having polar groups in an acid-decomposable resin is preferably from 1 to 40 mole %, far preferably from 5 to 30 mole %, further preferably from 5 to 20 mole %, of the total repeating structural units.

In the resin for use in the invention, the content of repeating structural units based on monomers as additional copolymerizing components can also be chosen appropriately according to the intended resist performance. In general, the proportion of such repeating structural units is preferably 99 mole % or below, far preferably 90 mole % or below, further preferably 80 mole % or below, based on the total mole number of the repeating structural units having alicyclic hydrocarbon-containing partial structures represented by the formulae (pI) to (pV) and the repeating units represented by the formula (II-AB).

When the present resist composition for negative development is designed for ArF exposure use, it is advantageous for the resin used therein to have no aromatic group in point of transparency to ArF light.

As to the alicyclic hydrocarbon-containing acid-decomposable resin for use in the invention, it is preferable that (meth)acrylate repeating units constitute all the repeating units of the resin. Herein, all the repeating units may be either acrylate repeating units, or methacrylate repeating units, or mixed acrylate-and-rnethacrylate repeating units. However, it is preferable that the acrylate repeating units is at most 50 mole % of the total repeating units.

The alicyclic hydrocarbon-containing acid-decomposable resin is preferably a copolymer having (meth)acrylate repeating units of three types: a type of having at least a lactone ring, a type of having an organic group substituted with at least either hydroxyl or cyano group, and a type of having an acid-decomposable group.

The alicyclic hydrocarbon-containing acid-decomposable resin is far preferably a ternary copolymer containing 20-50 mole % of repeating units having alicyclic hydrocarbon-containing partial structures represented by any of the formulae (pI) to (pV), 20-50 mole % of repeating units having lactone structures and 5-30 mole % of repeating units having alicyclic hydrocarbon structures substituted with polar groups, or a quaternary copolymer further containing 0-20 mole % of other repeating units.

The resin preferred in particular is a ternary copolymer containing 20-50 mole % of repeating units containing acid-decomposable groups, which are represented by any of the following formulae (ARA-1) to (ARA-7), 20-50 mole % of repeating units containing lactone groups, which are represented by any of the following formulae (ARL-1) to (ARL-7), and 5-30 mole % of repeating units having alicyclic hydrocarbon structures substituted with polar groups, which are represented by any of the following formulae (ARH-1) to (ARH-3), or a quaternary copolymer further containing 5-20 mole % of repeating units having carboxyl groups or structures represented by the formula (F1), or repeating units having alicyclic hydrocarbon structures but not showing acid decomposability.

In the following formulae, R_(xy1) represents a hydrogen atom or a methyl group, R_(xa1) and R_(xb1) each represent a methyl group or an ethyl group independently, and Rxe1 represents a hydrogen atom or a methyl group.

In the following formulae, R_(xy1) represents a hydrogen atom or a methyl group, R_(xd1) represents a hydrogen atom or a methyl group, and R_(xe1) represents a trifluoromethyl group, a hydroxyl group or a cyano group.

In the following formulae, R_(xy1) represents a hydrogen atom or a methyl group.

The alicyclic hydrocarbon-containing acid-decomposable resin for use in the invention can be synthesized according to general methods (e.g., radical polymerization). As examples of a general synthesis method, there are known a batch polymerization method in which polymerization is carried out by dissolving monomer species and an initiator in a solvent and heating them, and a drop polymerization method in which a solution containing monomer species and an initiator is added dropwise to a heated solvent over 1 to 10 hours. However, it is preferred that the drop polymerization method be used. Examples of a solvent usable in the polymerization reaction include ethers, such as tetrahydrofuran, 1,4-dioxane and diisopropyl ether; ketones, such as methyl ethyl ketone and methyl isobutyl ketone; ester solvents, such as ethyl acetate; amide solvents, such as dimethylformamide and dimethylacetamide; and solvents described hereafter which can dissolve the present composition, such as propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether and cyclohexanone. It is preferable that the polymerization is carried out using the same solvent as used for the present resist composition. By doing so, it becomes possible to prevent particles from developing during storage.

The polymerization reaction is preferably carried out in an atmosphere of inert gas, such as nitrogen or argon. And the polymerization is initiated using a commercially available radical initiator (e.g., an azo-type initiator or peroxide) as polymerization initiator. The radical initiator is preferably an azo-type initiator, and more specifically, an azo-type initiator having an ester group, a cyano group or a carboxyl group.

Examples of such a preferred azo-type initiator include azobisisobutyronitrile, azobisdimethylvaleronitrile and dimethyl 2,2′-azobis(2-methylpropionate). An addition of such an initiator may be made in the course of polymerization or such an initiator may be added in several portions, if desired. After the conclusion of the reaction, the reaction solution is poured into a solvent, and the intended polymer is collected as a powder or a solid. The concentration of reacting species is from 5 to 50 mass %, preferably from 10 to 30 mass %, and the reaction temperature is generally from 10° C. to 150° C., preferably from 30° C. to 120° C., far preferably from 60° C. to 100° C.

The polymer thus synthesized can be purified by the same method as applicable in the case of Resin (X) described hereinafter. For the purification, a usual method is applicable, and examples thereof include a liquid-liquid extraction method in which residual monomers and oligomeric components are eliminated by washing with water or by combined use of appropriate solvents, a method of performing purification in a solution state, such as an ultrafiltration method in which only components of molecular weight lower than a specific value are extracted and eliminated, a reprecipitation method in which a resin solution is dripped into a poor solvent to result in coagulation of the resin and elimination of residual monomers and so on, and a method of performing purification in a solid state, such as a method of washing filtered resin slurry with a poor solvent.

As to the resin relating to the invention, the weight average molecular weight thereof is preferably from 1,000 to 200,000, far preferably from 1,000 to 20,000, particularly preferably from 1,000 to 15,000, as measured by GPC and calculated in terms of polystyrene. By adjusting the weight average molecular weight to fall within the range of 1,000 to 200,000, declines in heat resistance and dry etching resistance can be prevented, and besides, degradation in developability and film formability deterioration from an increased viscosity can be prevented.

The polydispersity (molecular weight distribution) of the resin used is generally from 1 to 5, preferably from 1 to 3, far preferably from 1.2 to 3.0, particularly preferably from 1.2 to 2.0. When the polydispersity is smaller, the resist pattern formed is the more excellent in resolution and resist profile, and besides, it has the smoother side wall and the better roughness quality.

The total amount of resins relating to the invention, which are mixed in the present resist composition, is from 50 to 99.9 mass %, preferably from 60 to 99.0 mass %, of the total solids in the resist composition.

In the invention, one kind of resin may be used, or two or more kinds of resins may be used in combination.

From the viewpoint of compatibility with a protective film composition, it is appropriate that the present alicyclic hydrocarbon-containing acid-decomposable resin, preferably the present resist composition, contain neither fluorine atom nor silicon atom.

(B) Compound Capable of Generating Acid Upon Irradiation with Actinic Ray or Radiation

The resist composition according to the invention contains a compound capable of generating an acid upon irradiation with an actinic ray or radiation (which is also referred to as “a photo-acid generator” or “Component (B)”).

The compound usable as such a photo-acid generator can be selected appropriately from photo-initiators for cationic photopolymerization, photo-initiators for radical photopolymerization, photodecoloring agents for dyes, photodiscoloring agents, compounds used in microresists and known to generate acids upon irradiation with an actinic ray or radiation, or mixtures of two or more thereof.

Examples of such compounds include diazonium salts, phosphonium salts, sulfonium salts, iodonium salts, imide sulfonate, oxime sulfonate, diazodisulfone, disulfone and o-nitrobenzylsulfonate.

In addition, polymeric compounds having such groups or compounds as to generate acids upon exposure to an actinic ray or radiation in a state of being introduced in their main or side chains can also be used. Examples of those polymeric compounds include the compounds as disclosed in U.S. Pat. No. 3,849,137, German Patent No. 3914407, JP-A-63-26653, JP-A-55-164824, JP-A-62-69263, JP-A-63-146038, JP-A-63-163452, JP-A-62-153853 and JP-A-63-146029.

Further, the compounds capable of generating acids by the action of light as disclosed in U.S. Pat. No. 3,779,778 and European Patent No. 126,712 can be used too.

Of the compounds capable of decomposing upon irradiation with an actinic ray or radiation to generate acids, compounds represented by the following formulae (ZI), (ZII) and (ZIII) respectively are preferable.

In the formula (ZI), R₂₀₁, R₂₀₂ and R₂₀₃ each represent an organic group independently.

X″ represents a non-nucleophilic anion, preferably a sulfonic acid anion, a carboxylic acid anion, a bis(alkylsulfonyl)amide anion, a tris(alkylsulfonyl)methide anion, BF₄, PF₆ or SbF₆, far preferably a carbon-containing organic anion.

Examples of an organic anion preferred as X- include organic anions represented by the following formulae.

In the above formulae, Rc₁ represents an organic group.

Examples of the organic group as Rc₁ include groups containing 1 to 30 carbon atoms, preferably alkyl groups and aryl groups, which each may be substituted, and groups formed by connecting two or more of those groups via one or more of linkage groups, such as a single bond, —O—, —CO₂—, —S—, —SO₃— and —SO₂N(Rd₁)-. Rd₁ represents a hydrogen atom or an alkyl group.

Rc₃, Rc₄ and Rc₅ each represent an organic group independently. Examples of organic groups preferred as Rc₃, Rc₄ and Rc₅ include the same organic groups as the preferred of Rc₁, especially 1-4C perfluoroalkyl groups.

Rc₃ and Rc₄ may combine with each other to form a ring. The group formed by combining Rc₃ with Rc₄ is an alkylene group or an arylene group, preferably a 2-4C perfluoroalkylene group.

The organic groups particularly preferred as Rc₁, Rc₃, Rc₄ and Rc₅ each are alkyl groups substituted with fluorine atoms or fluoroalkyl groups at their respective 1-positions and phenyl groups substituted with fluorine atoms or fluoroalkyl groups. By containing a fluorine atom or a fluoroalkyl group, the acid generated by irradiation with light can have high acidity to result in enhancement of the sensitivity. Likewise, the ring formation by combination of Rc₃ and Rc₄ allows an acidity increase of the acid generated by irradiation with light to result in enhancement of the sensitivity.

The number of carbon atoms in the organic group as R₂₀₁, R₂₀₂ and R₂₀₃ each is generally from 1 to 30, preferably from 1 to 20.

Two of R₂₀₁ to R₂₀₃ may combine with each other to form a ring structure, and the ring formed may contain an oxygen atom, a sulfur atom, an ester linkage, an amide linkage or a carbonyl group. Examples of a group formed by combining two of R₂₀₁, R₂₀₂ and R₂₀₃ include alkylene groups (such as a butylene group and a pentylene group).

Examples of organic groups as R₂₀₁, R₂₀₂ and R₂₀₃ include their corresponding groups in compounds (ZI-1), (ZI-2) and (ZI-3) illustrated below.

Additionally, the photo-acid generator may be a compound having two or more of structures represented by formula (ZI). For instance, the photo-acid generator may be a compound having a structure that at least one of R₂₀₁, R₂₀₂ and R₂₀₃ in one compound represented by formula (ZI) is united with at least one of R₂₀₁, R₂₀₂ and R₂₀₃ in another compound represented by formula (ZI).

Far preferred examples of a compound (ZI) include compounds (ZI-1), (ZI-2) and (ZI-3) explained blow.

The compound (Z1-1) is an arylsulfonium compound represented by the formula (ZI) wherein at least one of R₂₀₁ to R₂₀₃ is an aryl group, namely a compound having an arylsulfonium as its cation.

In such an arylsulfonium compound, all of R₂₀₁ to R₂₀₃ may be aryl groups, or one or two of R₂₀₁ to R₂₀₃ may be aryl groups and the remainder may be an alkyl group or a cycloalkyl group.

Examples of such an arylsulfonium compound include a triarylsulfonium compound, a diarylalkylsulfonium compound, an aryldialkylsulfonium compound, a diarylcycloalkylsulfonium compound and an aryldicycloalkylsulfonium compound.

The aryl group in the arylsulfonium compound is preferably an aryl group, such as a phenyl group or a naphthyl group, or a hetroaryl group, such as an indole residue or a pyrrole residue, far preferably a phenyl group or an indole residue. When the arylsulfonium compound has two or more aryl groups, the two or more aryl groups may be the same or different.

One or two alkyl groups which the arylsulfonium compound has as required are preferably 1-15C straight-chain or branched alkyl groups, with examples including a methyl group, an ethyl group, a propyl group, an n-butyl group, a sec-butyl group and a t-butyl group.

One or two cycloalkyl groups which the arylsulfonium compound has as required are preferably 3-15C cycloalkyl groups, with examples including a cyclopropyl group, a cyclobutyl group and a cyclohexyl group.

The aryl group, the alkyl group or the cycloalkyl group represented by any of R₂₀₁ to R₂₀₃ may have as a substituent an alkyl group (containing, e.g., 1 to 15 carbon atoms), a cycloalkyl group (containing, e.g., 3 to 15 carbon atoms), an aryl group (containing, e.g., 6 to 14 carbon atoms), an alkoxyl group (containing, e.g., 1 to 15 carbon atoms), a halogen atom, a hydroxyl group or a phenylthio group. Suitable examples of such substituents include 1-12C straight-chain or branched alkyl groups, 3-12C cycloalkyl groups and 1-12C straight-chain, branched or cyclic alkoxyl groups. Of these substituents, 1-4C alkyl groups and 1-4C alkoxyl groups are preferred over the others. One of R₂₀₁ to R₂₀₃ may have such a substituent, or all of R₂₀₁ to R₂₀₃ may have such substituents. When R₂₀₁ to R₂₀₃ are aryl groups, it is preferable that such a substituent is situated in the p-position of each aryl group.

Then, the compound (ZI-2) is explained below. The compound (ZI-2) is a compound represented by the formula (ZI) in which R₂₀₁ to R₂₀₃ each independently represent an organic group having no aromatic ring. The term “aromatic ring” as used herein is intended to also include aromatic rings containing hetero atoms.

The number of carbon atoms in an aromatic ring-free organic group as each of R₂₀₁ to R₂₀₃ is generally from 1 to 30, preferably from 1 to 20.

Each of R₂₀₁ to R₂₀₂ is preferably an alkyl group, a cycloalkyl group, an allyl group or a vinyl group, far preferably a straight-chain, branched or cyclic 2-oxoalkyl group, or an alkoxycarbonylmethyl group, particularly preferably a straight-chain or branched 2-oxoalkyl group.

The alkyl group as each of R₂₀₁ to R₂₀₃ may have either a straight-chain or branched form, and it is preferably a 1-10C straight-chain or branched group (e.g., a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group). The alkyl group as each of R₂₀₁ to R₂₀₃ is far preferably a straight-chain or branched 2-oxoalkyl group, or an alkoxycarbonylmethyl group.

The cycloalkyl group as each of R₂₀₁ to R₂₀₃ is preferably a 3-10C cycloalkyl group (e.g., a cyclopentyl group, a cyclohexyl group, a norbornyl group). The cycloalkyl group as each of R₂₀₁ to R₂₀₃ is far preferably a cyclic 2-oxoalkyl group.

Examples of a straight-chain, branched or cyclic 2-oxoalkyl group suitable as each of R₂₀₁ to R₂₀₃ include the groups having >C=0 in the 2-positions of the alkyl or cycloalkyl groups recited above.

The alkoxy moiety in an alkoxycarbonylmethyl group as each of R₂₀₁ to R₂₀₃ is preferably a 1-5C alkoxyl group (such as a methoxy, ethoxy, propoxy, butoxy or pentoxy group).

Each of groups represented by R₂₀₁ to R₂₀₃ may further be substituted with a halogen atom, an alkoxyl group (containing, e.g., 1 to 5 carbon atoms), a hydroxyl group, a cyano group or a nitro group.

The compound (ZI-3) is a compound represented by the following formula (ZI-3), namely a compound having a phenacylsulfonium salt structure.

In the formula (ZI-3), R_(1c) to R_(5c) each represent a hydrogen atom, an alkyl group, a cycloalkyl group, an alkoxyl group or a halogen atom independently.

R_(6c) and R_(7c) each represent a hydrogen atom, an alkyl group or a cycloalkyl group independently.

R_(x) and R_(y) each represent an alkyl group, a cycloalkyl group, an allyl group or a vinyl group independently.

Any two or more of R_(1c) to R_(7c) may combine with one another to form a ring structure, and R_(x) and R_(y) may also combine with each other to form a ring structure. In such a ring structure, an oxygen atom, a sulfur atom, an ester linkage or an amide linkage may be contained. The group formed by combining any two or more of R_(1c) to R_(7c) or by combining R_(x) and R_(y) may be a butylene group or a pentylene group.

X- represents a non-nucleophilic anion, and examples thereof include the same non-nucleophilic anions as examples of X- in formula (ZI) include.

The alkyl group as each of R_(1c) to R_(7c) may have either a straight-chain form or a branched form, and suitable examples thereof include 1-20C straight-chain or branched alkyl groups, preferably 1-12C straight-chain or branched alkyl groups (e.g., a methyl group, an ethyl group, a straight-chain or branched propyl group, straight-chain or branched butyl groups, straight-chain or branched pentyl groups).

Suitable examples of the cycloalkyl group as each of R_(1c) to R_(7c) include 3-8C cycloalkyl groups (e.g., a cyclopentyl group, a cyclohexyl group).

The alkoxyl group as each of R_(1c) to R_(5c) may have either a straight-chain form, or a branched form, or a cyclic form, and examples thereof include 1-10C alkoxyl groups, preferably 1-5C straight-chain and branched alkoxyl groups (e.g., a methoxy group, an ethoxy group, a straight-chain or branched propoxy group, straight-chain or branched butoxy groups, straight-chain or branched pentoxy groups) and 3-8C cycloalkoxyl groups (e.g., a cyclopentyloxy group, a cyclohexyloxy group).

It is preferable that any of Ric to R5c is a straight-chain or branched alkyl group, a cycloalkyl group, or a straight-chain, branched or cyclic alkoxyl group, and it is far preferable that the number of total carbon atoms in R_(1c), to R_(5c) is from 2 to 15. By meeting these requirements, the solvent solubility can be enhanced, and development of particles during storage can be prevented.

Examples of the alkyl group as each of R_(x) and R_(y) include the same groups as examples of the alkyl group as each of R_(1c) to R_(7c) include, preferably straight-chain and branched 2-oxoakyl groups and alkoxycarbonylmethyl groups.

Examples of the cycloalkyl group as each of R_(x) and R_(y) include the same groups as examples of the cycloalkyl group as each of R_(1c) to R_(7c) include, preferably cyclic 2-oxoakyl groups.

Examples of the straight-chain, branched and cyclic 2-oxoalkyl groups include the groups having >C═O at the 2-positions of the alkyl or cycloalkyl groups as R_(1c) to R_(7c).

Examples of the alkoxy moiety in the alkoxycarbonylmethyl group includes the same alkoxyl groups as R_(1c) to R_(5c) each may represent.

Each of R_(x) and R_(y) is preferably an alkyl group containing at least 4 carbon atoms, far preferably an alkyl group containing at least 6 carbon atoms, further preferably an alkyl group containing at least 8 carbon atoms.

In the formulae (ZII) and (ZIII), R₂₀₄ to R₂₀₇ each represent an aryl group, an alkyl group or a cycloalkyl group independently.

The aryl group as each of R₂₀₄ to R₂₀₇ is preferably a phenyl group or a naphthyl group, far preferably a phenyl group.

The alkyl group as each of R₂₀₄ to R₂₀₇ may have either a straight-chain form or a branched form, with suitable examples including 1-10C straight-chain and branched alkyl groups (e.g., a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group).

The cycloalkyl group as each of R₂₀₄ to R₂₀₇ is preferably a 3-10C cycloalkyl group (e.g., a cyclopentyl group, a cyclohexyl group, a norbomyl group).

The groups represented by R₂₀₄ to R₂₀₇ may have substituents. Examples of such substituents include alkyl groups (e.g., those containing 1 to 15 carbon atoms), cycloalkyl groups (e.g., those containing 3 to 15 carbon atoms), aryl groups (e.g., those containing 6 to 15 carbon atoms), alkoxyl groups (e.g., those containing 1 to 15 carbon atoms), halogen atoms, a hydroxyl group and a phenylthio group.

X—represents a non-nucleophilic anion, and examples thereof include the same non-nucleophilic anions as the X″ in the formula (ZI) can represent.

Of the compounds capable of generating an acid upon irradiation with an actinic ray or radiation, compounds represented by the following formulae (ZIV), (ZV) and (ZVI) can be preferred examples.

In the formulae (ZIV) to (ZVI), Ar₃ and Ar₄ each represent an aryl group independently.

R₂₂₆ represents an alkyl group, a cycloalkyl group or an aryl group.

R₂₂₇ and R₂₂₈ each represent an alkyl group, a cycloalkyl group, an aryl group or an electron-attracting group. R₂₂₇ is preferably an aryl group. R₂₂₈ is preferably an electron-attracting group, far preferably a cyano group or a fluoroalkyl group.

A represents an alkylene group, an alkenylene group or an arylene group.

Of the compounds capable of generating acids upon irradiation with an actinic ray or radiation, the compounds represented by (ZI) to (ZIII) are preferred to the others.

The Compound (B) is preferably a compound capable of generating an aliphatic sulfonic acid having a fluorine atom or atoms or a benzenesulfonic acid having a fluorine atom or atoms upon irradiation with an actinic ray or radiation.

It is preferable that the Compound (B) has a triphenylsulfonium structure.

It is far preferable that the Compound (B) is a triphenylsulfonium salt compound having in its cation part an alkyl or cycloalkyl group free of fluorine substituent.

Examples of particularly preferred ones among the compounds capable of generating acids upon irradiation with an actinic ray or radiation are illustrated below.

Photo-acid generators can be used alone or as combinations of two or more thereof. When two or more types of photo-acid generators are used in combination, it is preferable to combine compounds which can generate two types of organic acids differing by at least two in the total number of constituent atoms except hydrogen atoms.

The content of photo-acid generators is preferably from 0.1 to 20 mass %, far preferably from 0.5 to 10 mass %, further preferably from 1 to 7 mass %, based on the total solids in the resist composition. By adjusting the content of photo-acid generators to fall within the foregoing range, the exposure latitude at the time of resist pattern formation can be improved and the crosslinking reactivity with materials for forming a cross-linked layer can be increased.

(C) Solvent

Examples of a solvent which can be used in dissolving each of the ingredients to prepare a resist composition include organic solvents, such as an alkylene glycol monoalkyl ether carboxylate, an alkylene glycol monoalkyl ether, an alkyl lactate, an alkyl alkoxypropionate, a 4-10C cyclic lactone, a 4-10C monoketone compound which may contain a ring, an alkylene carbonate, an alkyl alkoxyacetate and an alkyl pyruvate.

Suitable examples of an alkylene glycol monoalkyl ether carbonate include propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, propylene glycol monobutyl ether acetate, propylene glycol monomethyl ether propionate, propylene glycol monoethyl ether propionate, ethylene glycol monomethyl ether acetate, and ethylene glycol monoethyl ether acetate.

Suitable examples of an alkylene glycol monoalkyl ether include propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether, and ethylene glycol monoethyl ether.

Suitable examples of an alkyl lactate include methyl lactate, ethyl lactate, propyl lactate, and butyl lactate.

Suitable examples of an alkyl alkoxypropionate include ethyl 3-ethoxypropionate, methyl 3-methoxypropionate, methyl 3-ethoxypropionate, and ethyl 3-methoxypropionate.

Suitable examples of a 4-10C cyclic lactone include (3-propiolactone, (3-butyrolactone, y-butyrolactone, a-methyl-y-butyrolactone, (3-methyl-y-butyrolactone, y-valerolactone, y-caprolactone, y-octanoic lactone, and a-hydroxy-y-butyrolactone.

Suitable examples of a 4-10C monoketone compound which may contain a ring include 2-butanone, 3-methylbutanone, pinacolone, 2-pentanone, 3-pentanone, 3-methyl-2-pentanone, 4-methyl-2-pentanone, 2-methyl-3-pentanone, 4,4-dimethyl-2-pentanone, 2,4-dimethyl-3-pentanone, 2,2,4,4-tetramethyl-3-pentanone, 2-hexanone, 3-hexanone, 5-methyl-3-hexanone, 2-heptanone, 3-heptanone, 4-heptanone, 2-methyl-3-heptanone, 5-methyl-3-heptanone, 2,6-dimethyl-4-heptanone, 2-octanone, 3-octanone, 2-nonanone, 3-nonanone, 5-nonanone, 2-decanone, 3-decanone, 4-decanone, 5-hexene-2-one, 3-pentene-2-one, cyclopentanone, 2-methylcyclopentanone, 3-methylcyclopentanone, 2,2-dimethylcyclopentanone, 2,4,4-trimethylcyclopentanone, cyclohexanone, 3-methylcyclohexanone, 4-methylcyclohexanone, 4-ethylcyclohexanone, 2,2-dimethylcyclohexanone, 2,6-dimethylcyclohexanone, 2,2,6-trimethylcyclohexanone, cycloheptanone, 2-methylcycloheptanone, and 3-methylcycloheptanone.

Suitable examples of an alkylene carbonate include propylene carbonate, vinylene carbonate, ethylene carbonate, and butylene carbonate.

Suitable examples of an alkyl alkoxyacetate include acetate-2-methoxyethyl, acetate-2-ethoxyethyl, acetate-2-(2-ethoxyethoxy)ethyl, acetate-3-methoxy-3-methylbutyl, and acetate-1-methoxy-2-propyl.

Suitable examples of an alkyl pyruvate include methyl pyruvate, ethyl pyruvate, and propyl pyruvate.

Examples of a solvent used to advantage include solvents having boiling points of 130° C. or above at ordinary temperatures and under normal atmospheric pressure. More specifically, such solvents include cyclopentanone, y-butyrolactone, cyclohexanone, ethyl lactate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, ethyl 3-ethoxypropionate, ethyl pyruvate, acetate-2-ethoxyethyl, acetate-2-(2-ethoxyethoxy)ethyl and propylene carbonate.

In the invention, the solvents recited above may be used alone or as combinations of two or more thereof.

The solvent used in the invention may also be a mixture of a solvent having a hydroxyl group in its structure and a solvent having no hydroxyl group.

Examples of a solvent having a hydroxyl group include ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, and ethyl lactate. Of these solvents, propylene glycol monomethyl ether and ethyl lactate are especially preferred to the others.

Examples of a solvent having no hydroxyl group include propylene glycol monomethyl ether acetate, ethyl ethoxypropionate, 2-heptanone, y-butyrolactone, cyclohexanone, butyl acetate, N-methylpyrrolidone, N,N-dimethylacetamide, and dimethyl sulfoxide. Of these solvents, propylene glycol monomethyl ether acetate, ethyl ethoxypropionate, 2-heptanone, y-butyrolactone, cyclohexanone and butyl acetate are far preferred to the others, and propylene glycol monomethyl ether acetate, ethyl ethoxypropionate and 2-heptanone are used to particular advantage.

The mixing ratio (by mass) between the solvent containing a hydroxyl group and the solvent containing no hydroxyl group is from 1/99 to 99/1, preferably from 10/90 to 90/10, far preferably from 20/80 to 60/40. A mixed solvent containing a solvent having no hydroxyl group in a proportion of 50 weight % or above is particularly preferred from the viewpoint of coating evenness.

The solvent used in the invention is preferably a mixture of two or more kinds of solvents including propylene glycol monomethyl ether acetate.

(E) Basic Compound

For reduction of performance changes occurring with the passage of time from exposure to heating, it is appropriate that the resist composition for use in the invention contain (E) a basic compound.

Examples of a compound suitable as the basic compound include compounds having structures represented by the following (A) to (E).

In the formulae (A) and (E), R²⁰⁰, R²⁰¹ and R²⁰² may be the same or different, and each of them represents a hydrogen atom, an alkyl group (preferably a 1-20C alkyl group), a cycloalkyl group (preferably a 3-20C cycloalkyl group) or an aryl group (containing 6 to 20 carbon atoms). Herein, R²⁰¹ and R²⁰² may combine with each other to form a ring.

When the foregoing alkyl group has a substituent, a 1-20C aminoalkyl group, a 1-20C hydroxyalkyl group or a 1-20C cyanoalkyl group is suitable as the substituted alkyl group.

In the formula (E), R²⁰³, R²⁰⁴, R²⁰⁵ and R²⁰⁶ may be the same or different, and each of them represents a 1-20C alkyl group.

The alkyl groups in the formulae (A) to (E) are preferably unsubstituted alkyl groups.

Examples of preferred basic compounds include guanidine, aminopyrrolidine, pyrazole, pyrazoline, piperazine, aminomorpholine, aminoalkylmorpholine and piperidine. Examples of far preferred compounds include compounds having an imidazole structure, a diazabicyclo structure, an onium hydroxide structure, an onium carboxylate structure, a trialkylamine structure, an aniline structure and a pyridine structure, respectively; an alkylamine derivative having a hydroxyl group and/or an ether linkage; and an aniline derivative having a hydroxyl group and/or an ether linkage.

Examples of the compound having an imidazole structure include imidazole, 2,4,5-triphenylimidazole and benzimidazole. Examples of the compound having a diazabicyclo structure include 1,4-diazabicyclo[2.2.2]octane, 1,5-diazabicyclo[4.3.0]nona-5-ene and 1,8-diazabicyclo[5.4.0]undeca-7-ene. Examples of the compound having an onium hydroxide structure include triarylsulfonium hydroxides, phenacylsulfonium hydroxides and sulfonium hydroxides having 2-oxoalkyl groups, and more specifically, they include triphenylsulfonium hydroxide, tris(t-butylphenyl)sulfonium hydroxide, bis(t-butylphenyl)iodonium hydroxide, phenacylthiophenium hydroxide and 2-oxopropylthiophenium hydroxide. The compound having an onium carboxylate structure is a compound having the structure corresponding to the substitution of carboxylate for the anion moiety of the compound having an onium hydroxide structure, with examples including acetate, adamantane-1-carboxylate and perfluoroalkylcarboxylates. Examples of the compound having a trialkylamine structure include tri(n-butyl)amine and tri(n-octyl)amine. Examples of the aniline compound include 2,6-diisopropylaniline, N,N-dimethylaniline, N,N-dibutylaniline and N,N-dihexylaniline. Examples of the alkylamine derivative having a hydroxyl group and/or an ether linkage include ethanolamine, diethanolamine, triethanolamine and tris(methoxyethoxyethyl)amine. An example of the aniline derivative having a hydroxyl group and/or an ether linkage is N,N-bis(hydroxyethyl)aniline.

These basic compounds are used alone or as combinations of two or more thereof.

The amount of basic compounds used is generally from 0.001 to 10 mass %, preferably 0.01 to 5 mass %, based on the total solids in the resist composition.

The ratio between the amount of acid generator(s) used and the amount of basic compound(s) used in the composition, the acid generator/basic compound ratio (by mole), is preferably from 2.5 to 300. More specifically, it is appropriate that the ratio by mole be adjusted to at least 2.5 in point of sensitivity and resolution, and that it be adjusted to at most 300 from the viewpoint of preventing degradation in resolution by thickening of resist patterns with the passage of time from the end of exposure to heating treatment. The acid generator/basic compound ratio (by mole) is preferably from 5.0 to 200, far preferably from 7.0 to 150.

(F) Surfactant

It is preferable that the resist composition for use in the invention further contains (F) a surfactant, specifically a surfactant containing at least one fluorine atom and/or at least one silicon atom (either a fluorine-containing surfactant, or a silicon-containing surfactant, or a surfactant containing both fluorine and silicon atoms), or a combination of at least two of these surfactants.

Incorporation of such a surfactant in the resist composition for use in the invention allows production of resist patterns having strong adhesion and reduced development defect while ensuring the composition both satisfactory sensitivity and high resolution in the case of using an exposure light source of 250 nm or below, especially 220 nm or below.

Examples of a surfactant containing at least one fluorine atom and/or at least one silicon atom include the surfactants disclosed in JP-A-62-36663, JP-A-61-226746, JP-A-61-226745, JP-A-62-170950, JP-A-63-34540, JP-A-7-230165, JP-A-8-62834, JP-A-9-54432, JP-A-9-5988, JP-A-2002-277862, and U.S. Pat. Nos. 5,405,720, 5,360,692, 5,529,881, 5,296,330, 5,436,098, 5,576,143, 5,294,511 and 5,824,451. In addition, the following commercially available surfactants can also be used as they are.

Examples of commercial surfactants which can be used include fluorine- or silicon-containing surfactants, such as EFTOP EF301 and EF303 (produced by Shin-Akita Kasei K.K.), Florad FC430, 431 and 4430 (produced by Sumitomo 3M, Inc.), Megafac F171, F173, F176, F189, F113, F110, F177, F120 and R08 (produced by Dainippon Ink & Chemicals, Inc.), Surflon S-382, SC101, 102, 103, 104, 105 and 106 (produced by Asahi Glass Co., Ltd.), Troysol S-366 (produced by Troy Chemical Industries, Inc.), GF-300 and GF-150 (produced by Toagosei Co., Ltd.), Surflon S-393 (produced by Seimi Chemical Co., Ltd.), EFTOP EF121, EF122A, EF122B, RF122C, EF125M, EF135M, EF351, EF352, EF801, EF802 and EF601 (produced by JEMCO Inc.), PF636, PF656, PF6320 and PF6520 (produced by OMNOVA Solutions Inc.), and FTX-204D, 208G, 218G, 230G, 204D, 208D, 212D, 218D and 222D (produced by NEOS). Moreover, organosiloxane polymer KP-341 (produced by Shin-Etsu Chemical Co., Ltd.) can be used as a silicon-containing surfactant.

In addition to the heretofore known surfactants as recited above, surfactants utilizing polymers having fluorinated aliphatic groups derived from fluorinated aliphatic compounds synthesized by a telomerization method (also referred to as a telomer method) or an oligomerization method (also referred to as an oligomer method) can be used. These fluorinated aliphatic compounds can be synthesized according to the methods disclosed in JP-A-2002-90991.

The polymers having fluorinated aliphatic groups are preferably copolymers of fluorinated aliphatic group-containing monomers and (poly(oxyalkylene)) acrylates and/or (poly(oxyalkylene)) methacrylates, wherein the fluorinated aliphatic group-containing units may be distributed randomly or in blocks. Examples of such a poly(oxyalkylene) group include a poly(oxyethylene) group, a poly(oxypropylene) group and a poly(oxybutylene) group. In addition, the poly(oxyalkylene) group may be a unit containing alkylene groups of different chain lengths in its oxyalkylene chain, such as poly(oxyethylene block/oxypropylene block/oxyethylene block combination) and poly(oxyethylene block/oxypropylene block combination). Further, the copolymers of fluorinated aliphatic group-containing monomers and (poly(oxyalkylene)) acrylates (or methacrylates) may be not only binary copolymers but also ternary or higher copolymers prepared using in each individual copolymerization at least two different kinds of fluorinated aliphatic group-containing monomers or/and at least two different kinds of (poly(oxyalkylene)) acrylates (or methacrylates) at the same time.

Examples of commercially available surfactants of such types include Megafac F178, F-470, F-473, F-475, F-476 and F-472 (produced by Dainippon Ink & Chemicals, Inc.). Additional examples of surfactants of such types include a copolymer of C6F13 group-containing acrylate (or methacrylate) and poly(oxyalkylene) acrylate (or methacrylate), and a copolymer of C3F7 group-containing acrylate (or methacrylate), poly(oxyethylene) acrylate (or methacrylate) and poly(oxypropylene) acrylate (or methacrylate).

Alternatively, it is also possible to use surfactants other than surfactants containing fluorine and/or silicon atoms. Examples of such surfactants include nonionic surfactants, such as polyoxyethylene alkyl ethers (e.g., polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, polyoxyethylene cetyl ether, polyoxyethylene oleyl ether), polyoxyethylene alkyl aryl ethers (e.g., polyoxyethylene octyl phenol ether, polyoxyethylene nonyl phenol ether), polyoxyethylene-polyoxypropylene block copolymers, sorbitan fatty acid esters (e.g., sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan monooleate, sorbitan trioleate, sorbitan tristearate), and polyoxyethylene sorbitan fatty acid esters (e.g., polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan trioleate, polyoxyethylene sorbitan tristearate).

These surfactants may be used alone or as combinations of two or more thereof.

The amount of a surfactant (F) used is preferably from 0.01 to 10 mass %, preferably 0.1 to 5 mass %, based on the total ingredients (exclusive of a solvent) in the resist composition.

(G) Onium Salt of Carboxylic Acid

The resist composition for use in the invention may further contain (G) an onium salt of carboxylic acid. Examples of such an onium salt of carboxylic acid (G) include sulfonium carboxylates, iodonium carboxylates and ammonium carboxylates. Of these onium salts, iodonium salts and sulfonium salts are especially preferred. In addition, it is preferable that neither aromatic group nor carbon-carbon double bond is present in the carboxylate residue of an onium carboxylate (G) used in the invention. As the anion part of (G), 1-30C straight-chain and branched alkyl carboxylate anions and mononuclear or polynuclear cycloalkyl carboxylate anions are especially suitable. Of these anions, the carboxylate anions whose alkyl groups are partially or entirely substituted with fluorine atoms are preferred over the others. In addition, those alkyl chains may contain oxygen atoms. Incorporation of an onium salt having such a carboxylate anion into a resist composition can ensure the resist composition transparency to light with wavelengths of 220 nm or below, and allows increases in sensitivity and resolution, and improvements in iso/dense bias and exposure margin.

Examples of a fluorinated carboxylate anion include a fluoroacetate anion, a difluoroacetate anion, a trifluoroacetate anion, a pentafluoropropionate anion, a heptafluorobutyrate anion, a nonafluoropentanate anion, a perfluorododecanate anion, a perfluorotridecanate anion, a perfluorocyclohexanecarboxylate anion and a 2,2-bistrifluoromethylpropionate anion.

The onium carboxylate (G) as recited above can be synthesized by allowing an onium hydroxide, such as sulfonium hydroxide, iodonium hydroxide or ammonium hydroxide, and a carboxylic acid to react with silver oxide in an appropriate solvent.

The suitable content of an onium salt of carboxylic acid (G) in a composition is generally from 0.1 to 20 mass %, preferably from 0.5 to 10 mass %, far preferably from 1 to 7 mass %, based on the total solids in the composition.

(H) Other Additives

The resist composition for use in the invention can further contain, on an as needed basis, dyes, plasticizers, photosensitizers, light absorbents, alkali-soluble resins, dissolution inhibitors and compounds which can promote dissolution in developers (e.g., phenol compounds having molecular weights of 1,000 or below, alicyclic or aliphatic compounds having carboxyl groups).

The phenol compounds which are 1,000 or below in molecular weight can be easily synthesized by persons skilled in the art when they refer to the methods as disclosed in JP-A-4-122938, JP-A-2-28531, U.S. Pat. No. 4,916,210 and European Patent No. 219,294.

Examples of alicyclic or aliphatic compounds having carboxyl groups include carboxylic acid derivatives having steroid structures, such as cholic acid, deoxycholic acid and lithocholic acid, adamantanecarboxylic acid derivatives, adamantanedicarboxylic acid, cyclohexanecarboxylic acid and cyclohexanedicarboxylic acid, but they are not limited to the compounds recited above.

A protective film composition for forming a protective film to be used in the pattern formation method of the invention is explained below.

<Protective Film Composition>

In the present pattern formation method, a film of protective film composition is formed on the top of a resist film prior to immersion exposure for the purpose of preventing direct contact between an immersion liquid and the resist film, thereby inhibiting resist performance degradation from the immersion liquid penetrated into the interior of the resist film and ingredients eluted from the resist film into the immersion liquid, and further for avoiding lens contamination with ingredients seeping out of the resist film into the immersion liquid.

For formation of a uniform film of protective film composition on the resist film, it is appropriate that a constituent resin of the protective film composition applied in the present pattern formation method be used in a state of being dissolved in a solvent.

For contribution to good-quality pattern formation without causing dissolution of resist film, it is appropriate that the protective film composition for use in the invention contain a solvent in which the resist film is insoluble, and it is more appropriate that the solvent used in the composition be different from the constituent solvent of a negative developer used. From the viewpoint of preventing elution into an immersion liquid, it is preferable that the composition is lower in immersion liquid solubility, and it is far preferable that the composition is lower in water solubility. The expression “lower in immersion liquid solubility” as used in the specification means being insoluble in the immersion liquid. Likewise, the expression “lower in water solubility” means being insoluble in water. In addition, from the viewpoints of volatility and coating suitability, it is preferable that the boiling point of the solvent in the composition is from 90° C. to 200° C.

To take an example from water solubility, the expression “lower in immersion liquid solubility” means that, when film formed by applying a protective film composition to a silicon wafer surface and drying the composition is immersed in purified water at 23° C. for 10 minutes and then dried, the reduction rate of film thickness is within 3% of the initial film thickness (typically 50 nm).

From the viewpoint of applying a uniform protective film, the solvent is used in an amount required for adjustment of the solids concentration to a range of 0.01 to 20 mass %, preferably 0.1 to 15 mass %, particularly preferably 1 to 10 mass %.

The solvent usable in the protective film composition has no particular restriction so long as it can dissolve Resin (X) described hereinafter, but it cannot dissolve the resist film. However, an alcohol solvent, a fluorinated solvent and a hydrocarbon solvent can be used to advantage, and a non-fluorinated alcohol solvent can be used to greater advantage. In such solvents, the resist film has further reduced solubility. So, application of the protective film composition to the resist film does not cause dissolution of the resist film, and a more uniform protective film can be formed.

In point of coating suitability, the alcohol solvent is preferably a monohydric alcohol, far preferably a monohydric 4-8C alcohol. The monohydric 4-8C alcohol may be of a straight-chain, branched or cyclic form, preferably a straight-chain or branched form. Examples of such an alcohol solvent include 1-butanol, 2-butanol, 3-methyl-1-butanol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol, 2-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 2-hexanol, 2-heptanol, 2-octanol, 3-hexanol, 3-heptanol, 3-octanol and 4-octanol. Of these alcohol solvents, 1-butanol, 1-hexanol, 1-pentanol and 3-methyl-1-butanol are preferred over the others.

Examples of a fluorinated solvent include 2,2,3,3,4,4-hexafluoro-1-butanol, 2,2,3,3,4,4,5,5-octafluoro-1-pentanol, 2,2,3,3,4,4,5,5,6,6-decafluoro-1-hexanol, 2,2,3,3,4,4-hexafluoro-1,5-pentanedio 1,2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol, 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoro-1,8-diol,2-fluoroanisole, 2,3-difluoroanisole, perfluorohexane, perfluoroheptane, perfluoro-2-pentanone, perfluoro-2-butyltetrahydrofuran, perfluorotetrahydrofuran, perfluorotributylamine, and perfluorotetrapentylamine. Of these solvents, the fluorinated alcohol solvents and the fluorinated hydrocarbon solvents are used to advantage.

Examples of the hydrocarbon solvent include aromatic hydrocarbon solvents, such as toluene, xylene and anisole, and aliphatic hydrocarbon solvents, such as n-heptane, n-nonane, n-octane, n-decane, 2-methylheptane, 3-methylheptane, 3,3-dimethylhexane and 2,3,4-trimethylpentane.

These solvents may be used alone or as combinations of two or more thereof.

When solvents other than those recited above are mixed, the proportion of the solvents mixed is generally from 0 to 30 mass %, preferably from 0 to 20 mass %, far preferably from 0 to 10 mass %, based on the total solvents in the protective film composition. By mixing with solvents other than those recited above, the solubility of the resist film, the solubility of the resin in the protective film composition and characteristics of elution from the resist film can be adjusted as appropriate.

For ensuring arrival of exposure light at the resist film via the protective film, it is appropriate that the resin be transparent to an exposure light source used. When ArF immersion exposure is adopted, it is preferable in point of transparency to ArF light that the resin has no aromatic group.

The resin is preferably a Resin (X) which has repeating units derived from a monomer containing either at least one fluorine atom, or at least one silicon atom, or both, far preferably a water-insoluble Resin (X′) which has repeating units derived from a monomer containing either at least one fluorine atom, or at least one silicon atom, or both. By having repeating units derived from a monomer containing either at least one fluorine atom, or at least one silicon atom, or both, the resin can attain good solubility in a negative developer, and the effects of the invention can be fully achieved.

The Resin (X) may contain fluorine atoms or silicon atoms in its main chain or in a state that those atoms are substituted for hydrogen atoms in its side chains. The Resin (X) is preferably a resin having as its partial structures fluorinated alkyl groups, fluorinated cycloalkyl groups or fluorinated aryl groups.

The fluorinated alkyl groups (preferably containing 1 to 10 carbon atoms, far preferably 1 to 4 carbon atoms) are straight-chain or branched alkyl groups which each have at least one fluorine atom substituted for a hydrogen atom, which may further have other substituents.

The fluorinated cycloalkyl groups are mononuclear or polynuclear cycloalkyl groups which each have at least one fluorine atom substituted for a hydrogen atom, which may further have other substituents.

The fluorinated aryl groups are aryl groups, such as a phenyl group and a naphthyl group, which each have a fluorine atom substituted for at least one hydrogen atom and may further have other substituents.

Examples of a fluorinated alkyl group, a fluorinated cycloalkyl group or a fluorinated aryl group are illustrated below, but these examples should not be construed as limiting the scope of the invention.

In the above formulae (f2) and (f3), R₅₇ to R₆₄ each represent a hydrogen atom, a fluorine atom or an alkyl group independently, provided that at least one of R₅₇ to R₆₁ and at least one of R₆₂ to R₆₄ are fluorine atoms or alkyl groups (preferably containing 1 to 4 carbon atoms) each having a fluorine atom substituted for at least one hydrogen atom. All of R₅₇ to R₆₁ are preferably fluorine atoms. Both R₆₂ and R₆₃ are preferably alkyl groups (preferably containing 1 to 4 carbon atoms) each having a fluorine atom substituted for at least one hydrogen atom, far preferably perfluoroalkyl groups having 1 to 4 carbon atoms. R₆₂ and R₆₃ may combine with each other to form a ring.

Examples of a group represented by the formula (f2) include a p-fluorophenyl group, a pentafluorophenyl group and a 3,5-di(trifluoromethyl)phenyl group.

Examples of a group represented by the formula (f3) include a trifluoroethyl group, a pentafluoropropyl group, a pentafluoroethyl group, a pentafluorobutyl group, a hexafluoroisopropyl group, a hexafluoro(2-methyl)isopropyl group, a nonafluorobutyl group, an octafluoroisobutyl group, a nonafluorohexyl group, a nonafluoro-t-butyl group, a perfluoroisopentyl group, a perfluorooctyl group, a perfluoro(trimethyl)hexyl group, a 2,2,3,3-tetrafluorocyclobutyl group and a perfluorohexyl group. Of these groups, a hexafluoroisopropyl group, a heptafluoroisopropyl group, a hexafluoro(2-methyl)isopropyl group, an octafluoroisobutyl group, a nonafluoro-t-butyl group and a perfluoroisopentyl group are preferable to the others, and a hexafluoroisopropyl group and a heptafluoroisopropyl group are far preferred.

The Resin (X) containing silicon atoms in its partial structures is preferably a resin having alkylsilyl structures (preferably trialkylsilyl groups) or cyclic siloxane structures as its partial structures.

Examples of an alkylsilyl or cyclic siloxane structure include groups represented by the following formula (CS-1), (CS-2) or (CS-3).

In the formulae (CS-1) to (CS-3), R₁₂ to R₂₆ are independent of one another, and each represent a straight-chain or branched alkyl group (preferably containing 1 to 20 carbon atoms) or a cycloalkyl group (preferably containing 3 to 20 carbon atoms).

L₃ to L₅ each represent a single bond or a divalent linkage group. Examples of such a divalent linkage group include an alkylene group, a phenylene group, an ether group, a thioether group, a carbonyl group, an ester group, an amide group, an urethane group, an urea group, and combinations of two or more of the groups recited above.

n represents an integer of 1 to 5.

An example of the Resin (X) is a resin having repeating units of at least one kind selected from among those represented by the following formulae (C-I) to (C-V).

In the formulae (C-I) to (C-V), R1 to R3 are independent of one another, and each represents a hydrogen atom, a fluorine atom, a 1-4C straight-chain or branched alkyl group, or a 1-4C straight-chain or branched fluoroalkyl group.

W₁ and W₂ each represent an organic group having at least either a fluorine atom or a silicon atom.

R₄ to R₇ are independent of one another, and each represents a hydrogen atom, a fluorine atom, a 1-4C straight-chain or branched alkyl group, or a 1-4C straight-chain or branched fluoroalkyl group; however at least one of the substituents R₄ to R₇ is required to be a fluorine atom. Alternatively, R₄ and R₅, or R₆ and R₇ may combine with each other to form a ring.

R₈ represents a hydrogen atom, or a 1-4C straight-chain or branched alkyl group.

R₉ represents a 1-4C straight-chain or branched alkyl group, or a 1-4C straight-chain or branched fluoroalkyl group.

L₁ and L₂ each represent a single bond or a divalent linkage group, which each have the same meaning as the foregoing L₃ to L₅ each have.

Q represents a mononuclear or polynuclear cyclic aliphatic group. More specifically, it represents atoms including two carbon atoms bonded together (C—C) and forming an alicyclic structure.

R₃₀ and R₃₁ each represent a hydrogen atom or a fluorine atom independently. R₃₂ and R₃₃ each represent an alkyl group, a cycloalkyl group, a fluorinated alkyl group or a fluorinated cycloalkyl group independently.

However, the repeating unit represented by the formula (C-V) is required to have at least one fluorine atom in at least one of the substituents R₃₀ to R₃₃.

It is preferable that the Resin (X) has repeating units represented by the formula (C-I), and it is far preferable that the Resin (X) has repeating units represented by the following formulae (C-Ia) to (C-Id).

In the formulae (C-Ia) to (C-Id), R₁₀ and R₁₁ each represent a hydrogen atom, a fluorine atom, a 1-4C straight-chain or branched alkyl group, or a 1-4C straight-chain or branched fluorinated alkyl group.

W₃ to W₆ each represent an organic group having at least either one or more fluorine atoms, or one or more silicon atoms.

When W₁ to W₆ are fluorine-containing organic groups, each organic group is preferably a 1-20C straight-chain, branched or cyclic fluorinated alkyl group, or a 1-20C straight-chain, branched or cyclic fluorinated alkoxyl group.

Examples of the fluorinated alkyl group of W₁ to W₆ each include a trifluoroethyl group, a pentafluoropropyl group, a hexafluoroisopropyl group, a hexafluoro(2-methyl)isopropyl group, a heptafluorobutyl group, a heptafluoroisopropyl group, an octafluoroisobutyl group, a nonafluorohexyl group, a nonafluoro-t-butyl group, a perfluoroisopentyl group, a perfluorooctyl group and a perfluoro(trimethyl)hexyl group.

When W₁ to W₆ are silicon-containing organic groups, each organic group preferably has an alkylsilyl or cyclic siloxane structure. Examples of such a group include groups represented by the formulae (CS-1), (CS-2) and (CS-3).

Examples of a repeating unit represented by the formula (C-I) are illustrated below. In the following structural formulae, X represents a hydrogen atom, —CH₃, —F or —CF₃.

The Resin (X) may further have repeating units represented by the following formula (Ia) for the purpose of adjusting its solubility in a negative developer.

In the formula (Ia), Rf represents a fluorine atom or a fluorinated alkyl group in which at least one hydrogen atom is substituted with a fluorine atom. R₁ represents an alkyl group. R₂ represents a hydrogen atom or an alkyl group.

The fluorinated alkyl group of Rf in the formula (Ia) is preferably a group containing 1 to 3 carbon atoms, far preferably a trifluoromethyl group.

The alkyl group of R₁ is preferably a 3-10C straight-chain or branched alkyl group, far preferably a 3-10C branched alkyl group.

The alkyl group of R₂ is preferably a 1-10C straight-chain or branched alkyl group, far preferably a 3-10C straight-chain or branched alkyl group.

Examples of a repeating unit represented by the formula (Ia) are illustrated below, but the invention should not be construed as being restricted by these examples.

X=F or CF₃

Furthermore, the Resin (X) may also have repeating units represented by the following formula (III).

In the formula (III), R₄ represents an alkyl group, a cycloalkyl group, an alkenyl group, a cycloalkenyl group, a trialkylsilyl group or a group having a cyclic siloxane structure, and L6 represents a single bond or a divalent linkage group.

The alkyl group of R₄ in the formula (III) is preferably a 3-20C straight-chain or branched alkyl group.

The cycloalkyl group is preferably a 3-20C cycloalkyl group.

The alkenyl group is preferably a 3-20C alkenyl group.

The cycloalkenyl group is preferably a 3-20C cycloalkenyl group.

The trialkylsilyl group is preferably a 3-20C trialkylsilyl group.

The group having a cyclic siloxane structure is preferably a group having a 3-20C cyclic siloxane structure.

The divalent linkage group of L₆ is preferably an alkylene group (preferably containing 1 to 5 carbon atoms) or an oxy group (—O—).

The Resin (X) may have lactone groups, ester groups, acid anhydride groups, and groups similar to the acid-decomposable groups in a Resin (A). The Resin (X) may further have repeating units represented by the following formula (VIII).

In the formula (VIII), Z₂ represents —O— or —N(R₄₁)—. R₄₁ represents a hydrogen atom, a hydroxyl group, an alkyl group or —OSO₂—R₄₂. R₄₂ represents an alkyl group, a cycloalkyl group or a camphor residue. The alkyl groups of R₄₁ and R₄₂ may be substituted with halogen atoms (preferably fluorine atoms) or so on.

It is preferable that the Resin (X) has repeating units (d) derived from a monomer containing an alkali-soluble group. Introduction of such repeating units allows control of immersion liquid solubility and coating solvent solubility of the Resin (X). Examples of the alkali-soluble group include groups containing a phenolic hydroxyl group, a carboxylic acid group, a fluorinated alcohol group, a sulfonic acid group, a sulfonamido group, a sulfonylimido group, an (alkylsulfonyl)(alkylcarbonyl)methylene group, an (alkylsulfonyl)(alkylcarbonyl)imido group, a bis(alkylcarbonyl)methylene group, a bis(alkylcarbonyl)imido group, a bis(alkylsulfonyl)methylene group, a bis(alkylsulfonyl)imido group, a tris(alkylcarbonyl)methylene group and a tris(alkylsulfonyl)methylene group.

The monomer containing an alkali-soluble group is preferably a monomer whose acid dissociation index pKa is 4 or above, far preferably a monomer whose pKa is from 4 to 13, and especially preferably a monomer whose pKa is from 8 to 13. When the Resin (X) has repeating units derived from a monomer whose pKa is 4 or above, swelling of the protective film during both negative development and positive development is restrained, and good developability is achieved in not only the case of using a negative developer but also the case of using a weak-base alkali developer as a positive developer.

Data on the acid dissociation constant Ka can be found in Kagaku Binran (II) (Handbook of Chemistry), revised 4th Ed., edited by The Chemical Society of Japan, published by Maruzen Co., Ltd. in 1993, and the pKa values of monomers containing alkali-soluble groups can be measured at 25° C., e.g., by use of an infinite dilution solvent.

Monomers having pKa of 4 or above are not limited to particular ones, and they may include monomers having acid groups (alkali-soluble groups), such as a phenolic hydroxyl group, a sulfonamido group, a —COCH2CO— group, a fluoroalcohol group and a carboxylic acid group. Of these monomers, a monomer having a fluoroalcohol group is particularly preferable to the others. The fluoroalcohol group is a fluoroalkyl group substituted with at least one hydroxyl group, which contains preferably 1 to 10 carbon atoms, far preferably 1 to 5 carbon atoms. Examples of such a fluoroalcohol group include —CF₂OH, —CH₂CF₂OH, —CH₂CF₂CF₂OH, —C(CF₃)₂OH, —CF₂CF(CF₃)OH, and —CH₂C(CF₃)₂OH. Of these fluoroalcohol groups, hexafluoroisopropanol group in particular is preferred.

The total proportion of repeating units derived from monomers containing alkali-soluble groups in the Resin (X) is preferably from 0 to 90 mole %, far preferably from 0 to 80 mole %, further preferably from 0 to 70 mole %, with respect to all the repeating units constituting the Resin (X).

A monomer having an alkali-soluble group may contain one acid group or more than one acid group. The number of acid groups contained in each of repeating units derived from such a monomer is preferably 2 or more, far preferably from 2 to 5, particularly preferably 2 or 3.

Suitable examples of a repeating unit derived from a monomer having an alkali-soluble group include, but not limited to, the repeating units illustrated below.

The Resin (X) is preferably a resin selected from the following resins (X-1) to (X-8).

(X-1): A resin that has (a) repeating units containing fluoroalkyl groups (which each preferably contain 1 to 4 carbon atoms), preferably a resin constituted of the repeating units (a) alone.

(X-2): A resin that has (b) repeating units containing trialkylsilyl groups or cyclic siloxane structures, preferably a resin having only the repeating units (b).

(X-3): A resin that has (a) repeating units containing fluoroalkyl groups (which each preferably contain 1 to 4 carbon atoms) and (c) repeating units containing branched alkyl groups (which each preferably contain 4 to 20 carbon atoms), cycloalkyl groups (which each preferably contain 4 to 20 carbon atoms), branched alkenyl groups (which each preferably contain 4 to 20 carbon atoms), cycloalkenyl groups (which each preferably contain 4 to 20 carbon atoms) or aryl groups (which each preferably contain 4 to 20 carbon atoms), preferably a copolymer resin constituted of the repeating units (a) and the repeating units (c).

(X-4): A resin that has (b) repeating units containing trialkylsilyl groups or cyclic siloxane structures and (c) repeating units containing branched alkyl groups (which each preferably contain 4 to 20 carbon atoms), cycloalkyl groups (which each preferably contain 4 to 20 carbon atoms), branched alkenyl groups (which each preferably contain 4 to 20 carbon atoms), cycloalkenyl groups (which each preferably contain 4 to 20 carbon atoms) or aryl groups (which each preferably contain 4 to 20 carbon atoms), preferably a copolymer resin constituted of the repeating units (b) and the repeating units (c).

(X-5): A resin that has (a) repeating units containing fluoroalkyl groups (which each preferably contain 1 to 4 carbon atoms) and (b) repeating units containing trialkylsilyl groups or cyclic siloxane structures, preferably a copolymer resin constituted of the repeating units (a) and the repeating units (b).

(X-6): A resin that has (a) repeating units containing fluoroalkyl groups (which each preferably contain 1 to 4 carbon atoms), (b) repeating units containing trialkylsilyl groups or cyclic siloxane structures and (c) repeating units containing branched alkyl groups (which each preferably contain 4 to 20 carbon atoms), cycloalkyl groups (which each preferably contain 4 to 20 carbon atoms), branched alkenyl groups (which each preferably contain 4 to 20 carbon atoms), cycloalkenyl groups (which each preferably contain 4 to 20 carbon atoms) or aryl groups (which each preferably contain 4 to 20 carbon atoms), preferably a copolymer resin constituted of the repeating units (a), the repeating units (b) and the repeating units (c).

Into the repeating units (c) which are contained in each of the resins (X-3), (X-4) and (X-6) and have branched alkyl groups, cycloalkyl groups, branched alkenyl groups, cycloalkenyl groups or aryl groups, appropriate functional groups can be introduced with consideration given to a balance between hydrophilic and hydrophobic properties and mutual interactivity.

(X-7): A resin that has (d) repeating units containing alkali-soluble groups (preferably repeating units containing alkali-soluble groups whose pKa values are 4 or above) in addition to the repeating units constituting each of the resins (X-1) to (X-6).

(X-8): A resin that has only the repeating units (d) whose alkali-soluble groups include fluorinated alcohol groups.

In the resins (X-3), (X-4), (X-6) and (X-7), the proportion of (a) repeating units containing fluoroalkyl groups, or the proportion of (b) repeating units containing trialkylsilyl groups or cyclic siloxane structures, or the total proportion of the repeating units (a) and the repeating units (b) is preferably from 10 to 99 mole %, far preferably from 20 to 80 mole %.

By having the alkali-soluble group-containing repeating units (d) in the resin (X-7), stripping by use of not only a negative developer but also other liquid removers, such as the case of using an alkaline aqueous solution as liquid remover, becomes easier.

The Resin (X) is preferably in a solid state at room temperature (25° C.), and the glass transition temperature (Tg) thereof is preferably from 50° C. to 200° C., far preferably from 80° C. to 160° C.

The expression “to be in a solid state at 25° C.” is intended to have a melting point of 25° C. or higher.

The glass transition temperature (Tg) can be measured with a differential scanning calorimeter, and can be determined, e.g., by analyzing specific volume variations occurring when a sample temperature is raised once, then the sample is cooled, and further a temperature rise at a rate of 5° C./min is carried out.

It is appropriate that the Resin (X) be insoluble in an immersion liquid (preferably water) but soluble in a negative developer (preferably a developer containing an organic solvent, far preferably a developer containing an ester solvent). From the viewpoint of stripping-off capabilities at the time of development with a positive developer, it is preferable that the Resin (X) is also soluble in an alkali developer.

When Resin (X) contains silicon atoms, the silicon content therein is preferably from 2 to 50 mass %, far preferably from 2 to 30 mass %, with respect to the molecular weight of the Resin (X). And the proportion of silicon-containing repeating units in the Resin (X) is preferably from 10 to 100 mass %, far preferably from 20 to 100 mass %.

Adjusting the silicon content and the proportion of silicon-containing repeating units in Resin (X) to fall within the ranges specified above allows the Resin (X) to have each of improved insolubility in an immersion liquid (preferably water), greater easiness of protective film stripping in the case of using a negative developer and improved incompatibility with resist film.

When Resin (X) contains fluorine atoms, the fluorine content therein is preferably from 5 to 80 mass %, far preferably from 10 to 80 mass %, with respect to the molecular weight of the Resin (X). And the proportion of fluorine-containing repeating units in the Resin (X) is preferably from 10 to 100 mass %, far preferably from 30 to 100 mass %.

Adjusting the fluorine content and the proportion of fluorine-containing repeating units in Resin (X) to fall within the ranges specified above allows the Resin (X) to have each of improved insolubility in an immersion liquid (preferably water), greater easiness of protective film stripping in the case of using a negative developer and improved incompatibility with resist film.

The weight average molecular weight of Resin (X) calculated in terms of standard polystyrene is preferably from 1,000 to 100,000, far preferably from 1,000 to 50,000, further preferably from 2,000 to 15,000, particularly preferably from 3,000 to 15,000.

From the viewpoint of reducing elution from the protective film into an immersion liquid, it is only natural that the content of impurities, such as metal, in Resin (X) is low, and besides, the content of monomer residues in Resin (X) is reduced preferably to 10 mass % or below, far preferably to 5 mass % or below, further preferably to I mass % or below. In addition, the molecular weight distribution (Mw/Mn, referred to as polydispersity) of Resin (X) is adjusted preferably to a range of 1 to 5, far preferably to a range of 1 to 3, further preferably to a range of 1 to 1.5.

Various products on the market can be utilized as Resin (X), and it is also possible to synthesize Resin (X) according to a general method (e.g., radical polymerization). As examples of a general synthesis method, there are known a batch polymerization method in which polymerization is carried out by dissolving monomer species and an initiator in a solvent and heating them, and a drop polymerization method in which a solution containing monomer species and an initiator is added dropwise to a heated solvent over 1 to 10 hours. However, it is preferred that the drop polymerization method be used. Examples of a solvent usable in the polymerization reaction include ethers, such as tetrahydrofuran, 1,4-dioxane and diisopropyl ether; ketones, such as methyl ethyl ketone and methyl isobutyl ketone; ester solvents, such as ethyl acetate; amide solvents, such as dimethylformamide and dimethylacetamide; and solvents as described hereafter, which can dissolve the present composition, such as propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether and cyclohexanone.

The polymerization reaction is preferably carried out in an atmosphere of inert gas, such as nitrogen or argon. And the polymerization is initiated using a commercially available radical initiator (e.g., an azo-type initiator or peroxide) as polymerization initiator. The radical initiator is preferably an azo-type initiator, and more specifically, an azo-type initiator having an ester group, a cyano group or a carboxyl group.

Examples of such a preferred azo-type initiator include azobisisobutyronitrile, azobisdimethylvaleronitrile and dimethyl 2,2′-azobis(2-methylpropionate). It is also possible to use a chain transfer agent as required. The concentration of reaction species is generally from 5 to 50 mass %, preferably from 20 to 50 mass %, far preferably from 30 to 50 mass %, and the reaction temperature is generally from 10° C. to 150° C., preferably from 30° C. to 120° C., far preferably from 60° C. to 100° C.

After the reaction is completed, the reaction product is allowed to stand and cooled to room temperature, and then subjected to purification. For the purification, a usual method is applicable, and examples thereof include a liquid-liquid extraction method in which residual monomers and oligomeric components are eliminated by washing with water or by combined use of appropriate solvents, a method of performing purification in a solution state, such as an ultrafiltration method in which only components of molecular weight lower than a specific value are extracted and eliminated, a reprecipitation method in which a resin solution is dripped into a poor solvent to result in coagulation of the resin and elimination of residual monomers and so on, and a method of performing purification in a solid state, such as a method of washing filtered resin slurry with a poor solvent. For instance, the reaction solution is brought into contact with an at most 10-fold, preferably 10- to 5-fold, volume of solvent (poor solvent) in which the resin is slightly soluble or insoluble, thereby precipitating the intended resin as a solid.

As the solvent used in the operation of precipitation or reprecipitation from a polymer solution (precipitation or reprecipitation solvent), any solvent can serve so long as it is a poor solvent of the polymer. And the solvent to be used in such an operation can be selected appropriately from the following poor solvents according to the kind of the polymer. Specifically, the poor solvents include hydrocarbons (such as aliphatic hydrocarbons including pentane, hexane, heptane and octane; alicyclic hydrocarbons including cyclohexane and methylcyclohexane; and aromatic hydrocarbons including benzene, toluene and xylene); halogenated hydrocarbons (such as aliphatic halogenated hydrocarbons including methylene chloride, chloroform and carbon tetrachloride; and aromatic halogenated hydrocarbons including chlorobenzene and dichlorobenzene); nitro compounds (such as nitromethane and nitroethane); nitriles (such as acetonitrile and benzonitrile); ethers (such as linear ethers including diethyl ether, diisopropyl ether and dimethoxyethane; and cyclic ethers including tetrahydrofuran and dioxane); ketones (such as acetone, methyl ethyl ketone and diisobutyl ketone); esters (such as ethyl acetate and butyl acetate); carbonates (such as dimethyl carbonate, diethyl carbonate, ethylene carbonate and propylene carbonate); alcohols (such as methanol, ethanol, propanol, isopropyl alcohol and butanol); carboxylic acids (such as acetic acid); water: and mixed solvents containing the solvents recited above. Of these solvents, solvents containing at least alcohol (especially methanol) or water are preferred as precipitation or reprecipitation solvents. In such a mixed solvent containing at least a hydrocarbon, the ratio of alcohol (especially methanol) to other solvents (e.g., esters such as ethyl acetate, ethers such as tetrahydrofuran), the alcohol/other solvents ratio, by volume at 25° C. is preferably of the order of 10/90 to 99/1, far preferably of the order of 30/70 to 98/2, further preferably of the order of 50/50 to 97/3.

The amount of a precipitation or reprecipitation solvent used can be chosen appropriately with consideration given to efficiency and yield, and it is generally from 100 to 10,000 parts by mass, preferably from 200 to 2,000 parts by mass, far preferably from 300 to 1,000 parts by mass, per 100 parts by mass of polymer solution.

The bore of a nozzle used for feeding a polymer solution into a precipitation or reprecipitation solvent (poor solvent) is preferably 4 mmφ or below (e.g., 0.2 to 4 mmφ. And the linear speed at which a polymer solution is fed (dripped) into a poor solvent is, e.g., from 0.1 to 10 m/sec, preferably of the order of 0.3 to 5 m/sec.

The precipitation or reprecipitation is preferably carried out with stirring. Examples of stirring blades usable for stirring include a desk turbine, a fan turbine (including paddles), a curved-blade turbine, a feather turbine, blades of Phaudler type, blades of Bullmargin type, an angle-blade fan turbine, propellers, multistage-type blades, anchor-type (horseshoe-type) blades, gate-type blades, double ribbon-type blades and screws. It is preferable that the stirring is continued for additional 10 minutes or above, especially 20 minutes or above, after the polymer solution feed is completed. When the stirring time is insufficient, there occurs a case where the monomer content in polymer particles cannot be reduced properly Instead of using stirring blades, a polymer solution and a poor solvent may be mixed together by using a line mixer.

The precipitation or reprecipitation temperature can be chosen appropriately with consideration given to efficiency and operational ease, and it is usually from 0° C. to 50° C., preferably in the vicinity of room temperature (e.g., from, 20° C. to 35° C.). In order to perform the precipitation or reprecipitation operation, a commonly-used mixing vessel, such as a stirred tank, and a hitherto known process, such as a batch process or a continuous process, can be utilized.

The polymer particles precipitated or reprecipitated are generally subjected to solid-liquid separation, such as filtration or centrifugation, and then dried. Thus, the polymer particles are made available for use. The filtration is carried out using a solvent-resistant filtering material, preferably under a pressurized condition. The drying is performed at a temperature of the order of 30° C. to 100° C., preferably of the order of 30° C. to 50° C., under a normal pressure or a reduced pressure, preferably under a reduced pressure.

Additionally, resin once precipitated and separated out of its solution may be dissolved in a solvent again and brought into contact with a solvent in which the resin is slightly soluble or insoluble.

More specifically, it is acceptable to adopt a method which includes bringing a reaction solution after finishing radical polymerization reaction into contact with a solvent in which the polymer produced is slightly soluble or insoluble, thereby precipitating the polymer as resin (process step a), separating the resin from the solution (process step b), preparing a resin solution A by dissolving the resin in a solvent again (process step c), bringing the resin solution A into contact with a solvent, in which the resin is slightly soluble or insoluble, the volume of which is lower than 10 times, preferably no higher than 5 times, the volume of the resin solution A, thereby precipitating the resin as a solid (process step d), and separating the precipitated resin out of the resultant solution (process step e).

The solvent used when the resin solution A is prepared may be a solvent similar to the solvent used in dissolving monomer(s) for polymerization reaction, and it may be one and the same as or different from the solvent used in the polymerization reaction.

The protective film composition for use in the invention may further contain a surfactant.

The surfactant used has no particular restrictions, and any of anionic surfactants, cationic surfactants and nonionic surfactants can be used as long as they can ensure uniform film formation from the protective film composition and are soluble in the solvent of the protective film composition.

The amount of surfactants added is preferably from 0.001 to 20 mass %, far preferably from 0.01 to 10 mass %.

The surfactants may be used alone or as combinations of two or more thereof.

The surfactants suitable for use in the protective film composition can be chosen from, e.g., alkyl cationic surfactants, amide-type quaternary cationic surfactants, ester-type quaternary cationic surfactants, amine oxide surfactants, betaine surfactants, alkoxylate surfactants, fatty acid ester surfactants, amide surfactants, alcohol surfactants, ethylenediamine surfactants, or fluorine- and/or silicon-containing surfactants (fluorine-containing surfactants, silicon-containing surfactants and surfactants containing both fluorine and silicon atoms).

Examples of the surfactants as recited above include polyoxyethylene alkyl ethers, such as polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, polyoxyethylene cetyl ether and polyoxyethylene oleyl ether; polyoxyethylene alkyl aryl ethers, such as polyoxyethylene octyl phenol ether and polyoxyethylene nonyl phenol ether; polyoxyethylene-polyooxypropylene block copolymers; sorbitan fatty acid esters, such as sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan monooleate, sorbitan trioleate and sorbitan tristearate; and polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan trioleate and polyoxyethylene sorbitan tristearate. In addition, commercial surfactants recited below can also be used as they are.

Examples of commercial surfactants which can be used include fluorine- or silicon-containing surfactants, such as EFTOP EF301 and EF303 (produced by Shin-Akita Kasei K.K.), Florad FC430, 431 and 4430 (produced by Sumitomo 3M, Inc.), Megafac F171, F173, F176, F189, F113, F110, F177, F120 and R08 (produced by Dainippon Ink & Chemicals, Inc.), Surflon S-382, SC101, 102, 103, 104, 105 and 106 (produced by Asahi Glass Co., Ltd.), Troysol S-366 (produced by Troy Chemical Industries, Inc.), GF-300 and GF-150 (produced by Toagosei Co., Ltd.), Surflon S-393 (produced by Seimi Chemical Co., Ltd.), EFTOP EF121, EF122A, EF122B, RF122C, EF125M, EF135M, EF351, EF352, EF801, EF802 and EF601 (produced by JEMCO Inc.), PF636, PF656, PF6320 and PF6520 (produced by OMNOVA Solutions Inc.), and FTX-204D, 208G, 218G, 230G, 204D, 208D, 212D, 218D and 222D (produced by NEOS). In addition, organosiloxane polymer KP-341 (produced by Shin-Etsu Chemical Co., Ltd.) can be used as a silicon-containing surfactant.

EXAMPLES

The invention is illustrated below in greater detail by reference to the following examples, but these examples should not be construed as limiting the scope of the invention.

Synthesis Example 1 Synthesis of Resin (X1)

In 250 ml of propylene glycol monomethyl ether, 43.6 g (0.1 mole) of 4-[bis(trifluoromethyl)-hydroxymethyl]styrene is dissolved. To the resultant solution, 0.20 g of 2,2′-azobis(2,4-dimethylvaleronitrile) (V-65, trade name, a product of Wako Pure Chemical Industries, Ltd.) is added as a polymerization initiator. This solution is stirred for 4 hours at 70° C. in a stream of nitrogen. Thereafter, the reaction solution is poured into IL of hexane with vigorous stirring. Resin thus precipitated is washed with ion exchange water, filtered off, and dried in a vacuum. Thus, 39 g of white resin is obtained. The weight average molecular weight and polydispersity (Mw/Mn) of the thus obtained Resin (X1) are 7,500 and 1.65, respectively.

In the manners similar to the above, Resins (X2) to (X8) are synthesized.

Structural formulae of Resins (X2) to (X8) are illustrated below. The ratio (by mole) between structural units, weight average molecular weight and polydispersity of each resin are summarized in Table 1.

<Preparation of Protective Film Composition>

Each combination of ingredients shown in Table 1 is dissolved in its corresponding solvent shown in Table 1 in such an amount as to prepare a solution having a solids concentration of 2.5 mass %, and passed through a polyethylene filter having a pore size of 0.05 μm. Thereby, protective film compositions Tx1 to Tx8 are prepared.

Evaluation of Solubility of Protective Film Composition in Negative Developer:

On a 4-inch silicon wafer having undergone dehydration treatment with hexamethylsilazane, each of the protective film compositions shown in Table 1 is coated by means of a spin coater, and the coating solvent is dried by heating on a 120° C. hot plate for 60 seconds. Thus, 100 nm-thick protective film is formed. Each of the thus formed films is immersed in a 23° C. butyl acetate solution (negative developer) for a proper period of time, and a dissolution rate thereof is measured with a resist dissolution rate analyzer (RDA790, made by Litho Tech Japan Co., Ltd.) and the rate of dissolution of each protective film composition in the negative developer is calculated. Results obtained are shown in Table 1.

TABLE 1 Resin Ratio Weight between Average Molecular Protective Structural Molecular Weight Solvent Dissolution Film Units Weight Dispersity (weight Surfactant Rate Composition Code (mol %) (Mw) (Mw/Mn) ratio) (100 ppm) (nm/sec) Tx1 X1 100 7,500 1.65 SL-1 W-1 1 Tx2 X2 100 5,000 1.75 SL-1 W-1 2 Tx3 X3 50/50 5,200 1.82 SL-1/ W-2 90 SL-2 (70/30) Tx4 X4 50/50 10,000 1.65 SL-1 W-3 6 Tx5 X5 50/50 16,000 1.85 SL-3 Not 1 added Tx6 X6 35/65 6,000 1.65 SL-1 W-2 10 Tx7 X7 50/50 5,500 1.63 SL-1 W-1 15 Tx8 X8 70/30 4,200 1.71 SL-1 W-3 250

The symbols in Table 1 stand for the following compounds, respectively.

W-1: Megafac R08 (a surfactant containing both fluorine and silicon atoms, produced by Dainippon Ink & Chemicals, Inc.)

W-2: Organosiloxane polymer KP-341 (a silicon surfactant, produced by Shin-Etsu Chemical Co., Ltd.)

W-3: PF6320 (a fluorinated surfactant, produced by OMNOVA Solutions Inc.)

SL-1: 1-Butanol

SL-2: Perfluoro-2-butyltetrahydrofuran

SL-3: Propylene glycol monomethyl ether

Synthesis Example 2 Synthesis of Resin (Al)

In a stream of nitrogen, 20 g of 6:4 (by mass) solvent mixture of propylene glycol mnomethyl ether acetate and propylene glycol monomethyl ether is put in a three-necked flask and heated up to 80° C. (Solvent 1). A monomer mixture composed of y-butyrolactone methacrylate, hydroxyadamantane methacrylate and 2-methyl-2-adamantyl methacrylate in proportions of 40:25:35 by mass is added to a 6:4 (by mass) solvent mixture of propylene glycol mnomethyl ether acetate and propylene glycol monomethyl ether, thereby preparing a 22 mass % monomer solution (200 g). Further, an initiator V-601 (a product of Wako Pure Chemical Industries, Ltd.) is added to and dissolved in the monomer solution in an amount of 8 mol % based on the total monomers. The resultant solution is added dropwise to the Solvent 1 over 6 hours. After the conclusion of dropwise addition, reaction is made to continue at 80° C. for additional 2 hours. The reaction solution obtained is allowed to stand for cooling. Then, the reaction solution is poured into a mixture of 1,800 ml of hexane and 200 ml of ethyl acetate, and powdery matter thus precipitated is filtered off and dried, thereby yielding 37 g of Resin (Al). The weight average molecular weight and polydispersisty (Mw/Mn) of Resin (Al) thus obtained are 6,500 and 1.65, respectively.

In the manners similar to the above, Resins (A2) to (A8) are synthesized.

Structural formulae of Resins (A2) to (A8) are illustrated below. And the ratio (by mole) between structural units, weight average molecular weight and polydispersity of each resin are summarized in Table 2.

<Preparation of Resist Composition>

Each combination of ingredients shown in Table 2 is dissolved in its corresponding solvent shown in Table 2 in such an amount as to prepare a solution having a solids concentration of 6 mass %, and passed through a polyethylene filter having a pore size of 0.05 pm. Thereby, resist compositions Ra1 to Ra8 are prepared.

TABLE 2 Resin Acid Ratio Basic Generator Structure between Compound (parts (parts Structural (parts Solvent Resist by by Mw Units by Surfactant (ratio by Composition mass) mass) (Mw/Mn) (by mole) mass) (100 ppm) mass) Ra1 z62 A1 5,500 40/25/35 N-1 W-4 SL-5/SL-6 (5.0) (94.50) (1.65) (0.50) (70/30) Ra2 z57 A2 6,500 40/25/35 N-1 W-4 SL-5/SL-6 (5.0) (94.45) (1.65) (0.55) (70/30) Ra3 z59 A3 5,500 55/5/40 N-1 W-4 SL-5/SL-6 (3.2) (96.30) (1.65) (0.50) (70/30) Ra4 z74 A4 8,200 55/5/40 N-2 W-3 SL-5/SL-6 (4.5) (95.00) (1.68) (0.50) (60/40) Ra5 z76 A5 4,000 35/20/45 N-2 W-2 SL-5/SL-6 (6.5) (93.05) (1.71) (0.45) (90/10) Ra6 z16 A6 8,500 35/15/35/15 N-1 W-1 SL-5/SL-6 (5.0) (94.50) (1.85) (0.50) (80/20) Ra7 z8 A7 13,500 40/5/45/10 N-3 W-4 SL-5/SL-6 (6.3) (93.30) (1.75) (0.40) (50/50) Ra8 z63 A8 5,500 40/10/40/10 N-1 W-4 SL-5/SL-6 (4.8) (94.70) (1.65) (0.50) (70/30)

The symbols in Table 2 stand for the following compounds, respectively.

N-1: N,N-Diphenylaniline

N-2: Diazabicyclo[4.3.0]nonene

N-3: 4-Dimethylaminopyridine

W-1: Megafac F176 (a fluorinated surfactant, produced by Dainippon Ink & Chemicals, Inc.)

W-2: Megafac R08 (a surfactant containing both fluorine and silicon atoms, produced by Dainippon Ink & Chemicals, Inc.)

W-3: Organosiloxane polymer KP-341 (a silicon surfactant, produced by Shin-Etsu Chemical Co., Ltd.)

W-4: PF6320 (a fluorinated surfactant, produced by OMNOVA Solutions Inc.)

SL-5: Propylene glycol monomethyl ether acetate

SL-6: Propylene glycol monomethyl ether

By the methods mentioned hereinafter, evaluations are made using the thus prepared protective film compositions and resist compositions.

Example 1

An organic antireflective film ARC29A (a product of Nissan Chemical Industries, Ltd.) is applied to a silicon wafer surface, and baked at 205° C. for 60 seconds, thereby forming a 78 nm-thick antireflective film. On this film, the resist composition Ra1 is spin-coated, and baked at 120° C. for 60 seconds, thereby forming a 150 nm-thick resist film.

Then, the protective film composition Tx1 is spin-coated on the resist film, and baked at 90° C. for 60 seconds, thereby forming a 30 nm-thick protective film on the resist film.

The thus obtained wafer is subjected to immersion exposure via a mask for pattern formation, wherein purified water is used as an immersion liquid and PAS5500/1250i equipped with a lens of NA=0.85 (made by ASML) is used as an ArF excimer laser scanner. After the exposure, the wafer is spun at revs of 2,000 rpm, and thereby the water remaining on the wafer is removed. Then, the wafer is subjected successively to 60 seconds' heating at 120° C., 60 seconds' development (negative development) with butyl acetate (negative developer), thereby undergoing simultaneous removal of the protective film composition and soluble parts of the resist film, rinse with 1-hexanol, and 30 seconds' spinning at revs of 4,000 rpm. Thus, 150-nm (1:1) line-and-space resist patterns are formed.

Examples 2 to 8 and Comparative Example 1 Changes in Compositions of Resist Film and Protective Film

150-nm (1:1) Line-and-space patterns are formed in the same manner as in Example 1, except that the combination of resist and protective film compositions is changed to each of the combinations shown in Table 3.

Example 9 Carrying Out Negative Development after Positive Development

An organic antireflective film ARC29A (a product of Nissan Chemical Industries, Ltd.) is applied to a silicon wafer surface, and baked at 205° C. for 60 seconds, thereby forming a 78 nm-thick antireflective film. On this film, the resist composition Ra1 is spin-coated, and baked at 120° C. for 60 seconds, thereby forming a 150 nm-thick resist film.

Then, the protective film composition Tx1 is spin-coated on the resist film, and baked at 90° C. for 60 seconds, thereby forming a 30 nm-thick protective film on the resist film.

The thus obtained wafer is subjected to immersion exposure via a mask for pattern formation, wherein purified water is used as an immersion liquid and PAS5500/1250i equipped with a lens of NA=0.85 (made by ASML) is used as an ArF excimer laser scanner. After the exposure, the water remaining on the wafer is removed by spinning the wafer at revs of 2,000 rpm. Further, the wafer is heated at 120° C. for 60 seconds. Then, the wafer is subjected to 60 seconds' development (positive development) with an aqueous tetramethylammonium hydroxide solution (2.38 mass %) (positive developer), thereby undergoing simultaneous removal of the protective film composition and soluble portions of the resist film, and further to rinse with purified water. Thus, patterns with a pitch of 600 nm and a line width of 450 nm are formed. Next, the resultant wafer is subjected to 60 seconds' development (negative development) with butyl acetate (negative developer), further to rinse with 1-hexanol, and then to 30 seconds' spinning at revs of 4,000 rpm. Thus, 150-nm (1:1) line-and-space resist patterns are obtained.

Example 10 Carrying Out Positive Development after Negative Development

An organic antireflective film ARC29A (a product of Nissan Chemical Industries, Ltd.) is applied to a silicon wafer surface, and baked at 205° C. for 60 seconds, thereby forming a 78 nm-thick antireflective film. On this film, the resist composition Ra1 is spin-coated, and baked at 120° C. for 60 seconds, thereby forming a 150 nm-thick resist film.

Then, the protective film composition Tx1 is spin-coated on the resist film, and baked at 90° C. for 60 seconds, thereby forming a 30 nm-thick protective film on the resist film.

The thus obtained wafer is subjected to immersion exposure via a mask for pattern formation, wherein purified water is used as an immersion liquid and PAS5500/1250i equipped with a lens of NA=0.85 (made by ASML) is used as an ArF excimer laser scanner. After the exposure, the water remaining on the wafer is removed by spinning the wafer at revs of 2,000 rpm. Further, the wafer is heated at 120° C. for 60 seconds. Then, the wafer is subjected to 60 seconds' development (negative development) with butyl acetate (negative developer), thereby undergoing simultaneous removal of the protective film composition and soluble portions of the resist film, further to rinse with 1-hexanol, and then to 30 seconds' spinning at revs of 4,000 rpm. Thus, patterns with a pitch of 600 nm and a line width of 450 nm are formed. Next, the resultant wafer is subjected to 60 seconds' development (positive development) with an aqueous tetramethylammonium hydroxide solution (2.38 mass %) (positive developer), and further to rinse with purified water. Thus, 150-nm (1:1) line-and-space resist patterns are obtained.

Examples 11 to 20 and Comparative Examples 2 to 4 Change in Development Condition

150-nm (1:1) Line-and-space resist patterns are formed in the same manner as in Example 1, except that the combination of protective film composition, resist composition, negative developer and rinse liquid for negative development is changed to each of the combinations shown in Table 3.

In Comparative Examples 2 to 4, on the other hand, positive development alone is carried out in place of negative development. More specifically, each wafer is subjected to 60 seconds' development (positive development) with an aqueous tetramethylammonium hydroxide solution (2.38 mass %) (positive developer), thereby undergoing simultaneous removal of the protective film composition and soluble portions of the resist film, further to rinse with purified water, and then to 30 seconds' spinning at revs of 4,000 rpm.

Evaluation of Line Edge Roughness (LER)

A 150-nm (1:1) line-and-space pattern obtained in each of Examples 1 to 20 and Comparative Examples 1 to 4 is observed under a critical dimension scanning electron microscope (S-9260, made by Hitachi Ltd.), and the 150-nm line pattern is examined for distance from its edge line along the length direction to a base line, on which the edge line should be, at 50 different points on a 2-1.1 m edge segment. And standard deviation is determined from these distance measurements, and further 3a is calculated. The smaller the value thus calculated, the better the performance. Results obtained are shown in Table 3.

Evaluation of Development Defect After Negative Development

Wafer processing is performed according to the same methods as in Examples 1 to 20 and Comparative Examples 1 to 4, respectively, wherein the exposure is carried out so that 150-nm (1:1) line-and-space patterns are formed in 78 sections of each wafer plane. The total exposure area of each wafer plane is 205 cm². The number of development defects in each wafer with patterns is measured with a defect inspection system KLA2360 (made by KLA-Tencor Corporation), and the value obtained by dividing the measured number by the exposure area is defined as the development defect number (number of defects/cm²). Results obtained are shown in Table 3.

Development defect numbers (number of defects/cm²) of 1 or below signify good performance. More specifically, numeric values ranging from smaller than 1 to 0.6 and those ranging from smaller than 0.6 to 0.2 are ranked in ascending order of performance improvement. And development defect numbers greater than 1 signify poor performance.

TABLE 3 Protective Rinse liquid for Development Film Forming Resist Negative Developer Negative Development LER Defect Composition Composition (ratio by mass) (ratio by mass) (nm) Number Example 1 Tx1 Ra1 Butyl acetate 1-Hexanol 4.7 0.59 2 Tx2 Ra2 Butyl acetate 1-Hexanol 5.4 0.50 3 Tx3 Ra3 Butyl acetate 1-Hexanol 3.5 0.29 4 Tx4 Ra4 Butyl acetate 1-Hexanol 5.0 0.40 5 Tx5 Ra5 Butyl acetate 1-Hexanol 6.8 0.72 6 Tx6 Ra6 Butyl acetate 1-Hexanol 3.9 0.28 7 Tx7 Ra7 Butyl acetate 1-Hexanol 4.0 0.35 8 Tx8 Ra8 Butyl acetate 1-Hexanol 5.0 0.48 9 Tx1 Ra1 Butyl acetate 1-Hexanol 7.1 0.76 10 Tx1 Ra1 Butyl acetate 1-Hexanol 3.3 0.41 11 Tx1 Ra1 Butyl acetate 3-Methyl-1-butanol 4.6 0.27 12 Tx2 Ra1 Isoamyl acetate 1-Hexanol 3.2 0.23 13 Tx1 Ra1 Methyl isobutyl ketone 1-Hexanol 6.9 0.50 14 Tx2 Ra1 2-Hexanone 1-Hexanol 5.0 0.49 15 Tx3 Ra1 n-Butyl ether 1-Hexanol 4.3 0.32 16 Tx4 Ra1 Butyl acetate/2-Hexanone 1-Hexanol 5.4 0.45 (80/20) 17 Tx5 Ra1 Isoamyl acetate/n-Butyl ether 1-Hexanol 5.2 0.75 (70/30) 18 Tx6 Ra1 Isoamyl acetate 2-Heptanol 3.1 0.25 19 Tx7 Ra1 Isoamyl acetate Decane 4.3 0.35 20 Tx8 Ra1 Isoamyl acetate 2-Heptanol/Decane 5.1 0.55 (50/50) Comparative 1 Not used Ra1 Butyl acetate 1-Hexanol 12.2 1.56 Example 2 Tx4 Ra1 — — 10.8 1.66 3 Tx5 Ra1 — — 11.9 1.46 4 Tx6 Ra1 — — Absence of resolved pattern

The term “ratio by mass” as used in Table 3 means a mixture ratio by mass in the case of using two kinds of organic solvents in combination as a negative developer or a rinse liquid for negative development. Herein, the ratio by mass in the case of using an organic solvent singly as a negative developer or a rinse liquid for negative development is 100.

The vapor pressures and boiling points of the solvents used as developers and rinse liquids for negative development in Examples are listed in Table 4.

TABLE 4 Vapor Pressure Boiling Point Solvent Name (kPa, value at 20° C.) (° C.) Butyl acetate 1.2 126 Isoamyl acetate 0.53 142 Methyl isobutyl ketone 2.1 117-118 2-Hexanone 0.36 126-128 Methyl ethyl ketone 10.5  80 Dipropyl ether 8.33 88-90 n-Butyl ether 0.64 142 1-Hexanol 0.13 157 1-Heptanol 0.015 175 2-Heptanol 0.133 150-160 3-Methyl-1-butanol 0.4 132 Decane 0.17 174 Dodecane 0.04 216

As clearly seen from Examples, high-accuracy, fine patterns reduced in line edge roughness and prevented from causing development defect after development can be formed consistently from the negative resist compositions according to the invention.

According to the invention, it is possible to provide a method of forming patterns with high accuracy through the attainment of reduction in not only development defects appearing after development but also line edge roughness.

The entire disclosure of each and every foreign patent application from which the benefit of foreign priority has been claimed in the present application is incorporated herein by reference, as if fully set forth. 

What is claimed is:
 1. A protective film composition, comprising: a resin and a solvent, wherein the resin does not contain a repeating unit derived from a monomer containing an alkali-soluble group selected from the group consisting of a phenolic hydroxyl group, a carboxylic acid group, a fluorinated alcohol group, a sulfonic acid group, a sulfonamido group, and a sulfonylimido group, the resin contains a repeating unit derived from a monomer containing either at least one fluorine atom, or at least one silicon atom, or both, and a protective film formed by the protective film composition is insoluble in water.
 2. The protective film composition according to claim 1, wherein the protective film composition contains at least one solvent selected from the group consisting of an alcohol solvent, a fluorinated solvent and a hydrocarbon solvent.
 3. The protective film composition according to claim 1, wherein the protective film composition contains a monohydric alcohol having a carbon number of from 4 to
 8. 4. The protective film composition according to claim 1, wherein the protective film composition contains an aliphatic hydrocarbon solvent.
 5. The protective film composition according to claim 1, wherein the protective film composition contains a plurality of two or three solvents, and at least one solvent among the plurality of solvents is a solvent selected from the group consisting of an alcohol solvent, a fluorinated solvent and a hydrocarbon solvent.
 6. The protective film composition according to claim 1, wherein the protective film composition contains at least two solvents selected from the group consisting of an alcohol solvent, a fluorinated solvent and a hydrocarbon solvent.
 7. The protective film composition according to claim 1, wherein the resin has no aromatic group.
 8. The protective film composition according to claim 1, wherein the glass transition temperature of the resin is from 80° C. to 160° C.
 9. The protective film composition according to claim 1, wherein the content of monomer residues in the resin is 0 to 10 mass %.
 10. The protective film composition according to claim 1, wherein the resin contains a repeating unit containing an alicyclic hydrocarbon group.
 11. The protective film composition according to claim 1, wherein the resin contains a repeating unit containing a polycyclic hydrocarbon group.
 12. The protective film composition according to claim 1, wherein the resin contains a (meth)acrylate repeating unit containing a polycyclic hydrocarbon group at a side chain.
 13. The protective film composition according to claim 1, which further contains a surfactant.
 14. The protective film composition according to claim 1, wherein the receding contact angle of water with respect to the protective film formed by the protective film composition is from 50 degrees to 100 degrees.
 15. The protective film composition according to claim 1, wherein a rate of dissolution of the protective film formed by the protective film composition in a negative developer is from 1 nm/sec to 300 nm/sec.
 16. The protective film composition according to claim 1, wherein the resin only contains a repeating unit represented by formula (C-Ia):

wherein R₁₀ represents a hydrogen atom, a fluorine atom, a straight-chain or branched alkyl group having a carbon number of from 1 to 4, or a straight-chain or branched fluorinated alkyl group having a carbon number of from 1 to 4, W₃ represents an organic group having at least either one or more fluorine atoms, or one or more silicon atoms, and the organic group is a straight-chain or branched fluorinated alkyl group having a carbon number of from 1 to
 20. 17. A method of forming patterns, comprising: (a) coating a substrate with a resist composition, (b) forming a protective film on the resist film with the protective film composition according to claim 1 after forming the resist film and before exposing the resist film, (c) exposing the resist film and the protective film, and (d) performing development with a developer.
 18. The method of forming patterns according to claim 17, wherein the developer in the process (e) is an organic developer containing an organic solvent.
 19. The method of forming patterns according to claim 18, wherein the process (d) of performing development comprises a process of removing the protective film composition and soluble portions of the resist film at the same time. 